Prime numbers...
Indeed, base 60 (and base 360) are two that I considered back when I was trying to decide what was the best for us as a species.
Binary is right out - 101011100100101001 is much harder to remember/say/write/grok then 178473.
Base 16 is much more appealing and a good alternative, but not perfect. Only 2 4 8 evenly go into 16 (~28% of numbers on 2..15).
It is also a bit tricky to count on your hands with this, though there are ways around this - ie, having hand up and hand down be distinct and counting the four non-thumb fingers twice per hand. If this seems like a silly consideration, remember that our numbering system should be universal.
Because of its applications in computers, base 16 should be taught more extensively to math/science-minded students. Specifically I believe we should teach not just translation to base 10, but each of the fundamental asthmatic operations in base 16 as well.
Base 60 requires that we teach kids 60 unique symbols. Basically anyone with Dyscalculia would cry at the thought of that. It is appealing because it is highly factorable and dense, so for me it might well have been superior (I excel in mental arithmetic), but that would not be universal. Instantaneous recognition of the full range of characters is mandatory, and this would complicate matters. Furthermore, multiplication would require memorization of 3600 operations, rather then our current 100.
Base 12 represents the smallest deviation from an accepted, standard system that returns the highest reward. Relative to base 10 it has the following benefits:
Density (distinct numbers expressible per length, n) is increased by 1.2^n at the cost of only 2 (20%) additional characters.
It requires only 144 operations to remember for multiplication (44% increase). Compare to base 60's 3500% increase, and base 16's 156% increase.
I am not counting addition and subtraction here since learning and utilizing them is actually a bit more tricky of a beast. For example, consider how I first memorized subtracting b from a, when b>a: 3-8 = 0-(7-2). More generally: a-b = 0-( A - B ), where A is a's compliment to 10, and ditto for B and b. My point is that there are too many different paths to first learning the system for it to be something you can honestly anticipate - contrary to multiplication, where pattern recognition pays off big time.
40% of numbers on 2..11 go into 12 evenly. Compare to 25% of base 10 on 2..9, ~28% of base 16 on 2..15, and ~17% of base 60 on 2..59. This makes mental shortcuts for addition, multiplication, and modulus functions much easier in base 12.
A refutation of an alternative numbering scheme for base 60, presented in advance: using number representation systems that require you to perform even the simplest of mathematical calculations to resolve a number (ie, the Babylonian and Roman systems, amongst others) is bad because it switches how your brain is thinking mid-problem. When I look at 632,887 I know how much it is because I have memorized what is basically a linked list of 10 elements. Each element is clearly distinct in my brain and has unique mathematical and representational properties.
Consider this simple case of Roman numerals: XIV. In order to know that number as 14 you have to perform both mental subtraction and addition. If you have something like IXL * IXL it is not immediately obvious that the answer is equivalent to XXXVIII * XXXVIII + II * XXXVIII + I. This is easy to see in our modern base ten representation: 39*39 = 38*38+2*38+1 (think about the expansion of a square by one unit of width, and then, one unit of height). This is because IXL and XXXVIII don't look the least bit alike, despite only being one apart.
Even the more simple Babylonian method, and indeed all schema that use simple pictographic patterns to generate the next digit, have a serious downfall: it is easy to mistake X and X+1 because they look similar. 5 and 6 are the closest we come to making this error, and its something that has irked me for a long while. Depending on the system it may be that X and X+Y appear very similar, but it is a problem that crops up.
Using unique digits is far superior for humans, mere mortals as we may be, even if it restricts us from using larger bases.
Actually, while Im thinking about it, Ive always been of the opinion that street lights should not use circles, but other shapes as well. This is for the benefit of synaesthetic and colorblind drivers, who may not be able to immediately intuit semi-rare traffic light configurations. I once saw a single traffic light that was configured as so:
XX
X
X
I have also seen horizontally mounted four wide lights before (and any other number of unconventional configurations), and was initially unsure what direction I should read it.
In general, I feel that too little thought goes into thinking about how we can change standards to fit real world limitations that seem uncommon, but are actually pervasive within a certain scope (ie, a certain individual who ubiquitously faces a unique challenge, or a common failing of a standard system that effects all people under certain situations). I believe that while widespread adoption of a superior solution is difficult, it can be incrementally accomplished with careful application in situational-specific cases.
Now, sorry for the hijack, and what was this thread about again?
Just a relative pedestrian observation about prime numbers, that's all. Once I have some time, I'll work on the frequency analysis and see what relevant use it might provide. Just after it proved to work for the first hundred, it seems like something worth looking into further, even if only for my own amusement and mental exercise.
M.
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Very simple and preliminary frequency analysis, using the first five primes in their first ten permutations as an example:
2+2+3=7 prime
2+2+5=9 square
2+2+7=11 prime
2+2+11=15 pop
2+2+13=17 prime
2+2+17=21 pop
2+2+19=23 prime
2+2+23=27 cube
2+2+29=33 pop
2+2+31=35 pop
3+3+2=8 cube
3+3+5=11 prime
3+3+7=13 prime
3+3+11=17 prime
3+3+13=19 prime
3+3+17=23 prime
3+3+19=25 square
3+3+23=29 prime
3+3+29=35 pop
3+3+31=37 prime
5+5+2=12 *none
5+5+3=13 prime
5+5+7=17 prime
5+5+11=21 pop
5+5+13=23 prime
5+5+17=27 cube
5+5+19=29 prime
5+5+23=33 pop
5+5+29=39 pop
5+5+31=41 prime
7+7+2=16 square
7+7+3=17 prime
7+7+5=19 prime
7+7+11=25 square
7+7+13=27 cube
7+7+17=31 prime
7+7+19=33 pop
7+7+23=37 prime
7+7+29=43 prime
7+7+31=45 *none
11+11+2=24 *none
11+11+3=25 square
11+11+5=27 cube
11+11+7=29 prime
11+11+13=35 pop
11+11+17=39 pop
11+11+19=41 prime
11+11+23=45 *none
11+11+29=51 pop
11+11+31=53 prime
4 of 50 have no immediate significance (8%)*
5 of 50 are squares (10%)
5 of 50 are cubes (10%)
12 of 50 are products of primes (pop) (24%)
24 of 50 are prime numbers (48%)
So far, statistically significant.
*Thus far, all of these are the product of a prime and either a square or a cube.
M.
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Since I'm not versed in math, I'm sure this already has a name... but while it is not an absolute rule, doesn't this help refine the number set of those being examined as being prime numbers?
M.
When I saw this post, it reminded me of odd perfect numbers. The related conjecture states that all numbers can be uniquely "built up" by a very small set of rules. I'm not sure if this particular rule is part of any known set.
One is neither prime nor composite, it is the unit on which all other numbers are based.
I search or large primes, the best method available uses different bases and the conversion between bases to elucidate if it is prime. This is masked behind something like "number x is/is not a testiment for compositeness". These tests can give false negatives, so they are done for a large number of cleverly selected primes.
One way to preliminary investigate your point, is to try and figure out if more than one 2A + B generate the same prime number? If so, it may not hold great promise for screening numbers. With the size of prime number hunting today, both A and B would be equally difficult to determine prime/composite than the orignal number itself. If both A and B are known primes, it does not really help you unless it is the only possible combination of primes.
M.
From a number theoretic p.o.v. a statistical analysis is devoid of significance and validity. By the way, every integer is the product of primes and 1.
ruveyn
Which you have stated before, and why I leave the greater theory to others; an analysis can only show trend and applicability within the number set selected. When ultimately factored, all integers are the product of primes - perhaps more specifically, in this case I should have said that these were the product of two and only two primes. Your point has been made - thank you.
M.
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My thanks to all the wonderful members here; I will miss the opportunity to continue to learn and work with you.
For those who seek an alternative, it is coming.
So long, and thanks for all the fish!
Just btw, numbers which are the product of two (not necessarily distinct) primes are called semiprime.
http://en.wikipedia.org/wiki/Semiprime
There's a boinc project which is named: Primegrid. (see the link)
Interesting?
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CrimsonClown
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I'm sixteen, in tenth grade, and taking algebra II, so I don't know a lot of the stuff you're talking about, but I found a few patterns for prime numbers.
All non prime numbers ending with the diget seven MUST be divisible by three
All non prime numbers ending with the diget one are either 1) divisible by three, 2) a product of two numbers ending with the diget one, or 3) both.
everyone (besides my algebra II H teacher) knows the diget sum trick. I edited a little: take the number and find digets that add up to three, six, or nine and cross them out. if there's no numbers left it's divisible by three.
All non prime numbers are divisible by at least one prime number under it's squareroot
I believe that a prime number formula would work by seperating x into individual digets and evaluating those.
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The person who defined a sentence as a thought or idea was very simple minded.
Or he noticed the rest of the world was simple minded and knew he could get away with it.
A couple things... 77 is a non-prime which ends in seven and is not divisible by three.
Not sure what you mean by non-primes are divisible by the root of a prime; that doesn't make much sense to me.
M.
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CrimsonClown
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Gender: Male
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It's just a way to narrow down the numbers you have to divide by.
sqrt(200)=14, so you only have to check the numbers fourteen and under. you've probely heard this one before, I'm just not good at describing stuff.
another one is # of prime numbers under sqrt(x) is less than or equal to # of prime numbers above sqrt(x)
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The person who defined a sentence as a thought or idea was very simple minded.
Or he noticed the rest of the world was simple minded and knew he could get away with it.
N.B a better term for "non prime numbers" is "composite numbers", as it stresses the fact that the number has explicitly more than two divisors (itself and unity). It then excludes 0 and 1.
As M says, the first exception to this is 77 (7*11).
No. The first exception here would be 91 (7*13).
True, but it doesn't work the other way round. Here, the first exception is 57 = 3*19, where there are no digts that add up to 3, 6 or 9, but the number is divisible by 3.
The general rule you are after is just to add up all the digits. Repeat as many times asuor need, until yo have a single digit remaining. If that is 9, then the original number is divisible by 9. If the digit is 3 or 6, the original number was divisible by 3, but not divisible by 9.
E.g. 63554637 -> 39 -> 12 -> 3, so it is divisible by 3, but not 9.
(Actually, it is 3*383*55313).
Change that to "under or equal to". 9 is composite, and its square root is exactly 3. Or... 3059527969 is composite (same reason.... its square root happens to be an exact prime).
I'm unclear what you mean by "evaluating" them.
If you preserve their order, then the digits ARE the number.
If you lose the order of the digits, then they tell you only about about divisibility by 3 or 9.
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sqrt(200)=14, so you only have to check the numbers fourteen and under. you've probely heard this one before,
much better.
For every composite none square number each divisor under the square root of the number has a divisor over the square root of the number.
ruveyn
