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**Primenumbers****Member**- Registered: 2013-01-22
- Posts: 127

For prime numbers (p), under 3 squared; p = 2a + 1 (where a = any whole number)

For prime numbers (r), under 5 squared; r = 3p +/- 2 or 4

For prime numbers (i), under 7 squared; i = 5r +/- 6 or 12 or 18 or 24

For prime numbers (m), under 11 squared; m = 7i +/- 30 or 60 or 90 or 120 or 150 or 180

For prime numbers (e), under 13 squared; e = 11m +/- 210 or 420 or 630 or 840 or 1050 or 1260 or 1470 or 1680 or 1890 or 2100

(A no. divisible by a, but not divisible by a group b +/- A no. divisible by group b, but not a = A no. not divisible by a or b.)

* Some rules give 1 but this is not prime.

**"Time not important. Only life important."*** - The Fifth Element 1997*

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,018

Hi Primenumbers

Welcome to the forum!

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 107,776

Hi Primenumbers;

Welcome to the forum!

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**n872yt3r****Member**- Registered: 2013-01-21
- Posts: 392

Prime numbers are numbers that have no other factors then one and itself. One is not a prime number... 1x1=1 and 1/1=1.

x = prime

y = anything other than 1 and x

z = composite

a = decimal

x/1=x. x/x=1. x/y=a.

z/1=z. z/z=1. z/y=y.

For something else on prime numbers... go to my Sieve of Eratosthenes post.

- n872yt3r

Math Is Fun Rocks!

By the power of the exponent, I square and cube you!

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**cmowla****Member**- Registered: 2012-06-14
- Posts: 61

kerr wrote:

http://en.wikipedia.org/wiki/Largest_known_prime_number

How is 17,425,170 a prime number? It is divisible by 2.

Thanks

It clearly says in plain English that this number is the number of digits of the largest known prime number. You're welcome?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 107,776

Hi kerr;

is the prime number.**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**Primenumbers****Member**- Registered: 2013-01-22
- Posts: 127

2+/-1..

6+/-1 5..

30+/- 1 7..

210 +/- 1 11..

2310 +/- 1 13..

equals primes......to a certain point above highest prime squared. e.g.>9,25,49,121 or 169 accordingly. And so on but the numbers get very big but you can do this up to infinity.

**"Time not important. Only life important."*** - The Fifth Element 1997*

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**Primenumbers****Member**- Registered: 2013-01-22
- Posts: 127

The primes there are in a certain range can be estimated because there are;

1 No. not factorable by 2 in (2)

There are 2 No.'s not factorable by 2 or 3 in (6)

There are 8 No.'s not factorable by 2 or 3 or 5 in (30)

There are 48 No.'s not factorable by 2 or 3 or 5 or 7 or in (210)

times 48 by (prime -1) to get the next number of no.'s. i.e. =480 no.'s in (2310) not factorable by 2,3,5,7, or 11.....and so on.

**"Time not important. Only life important."*** - The Fifth Element 1997*

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**Gophne****Member**- Registered: 2016-10-16
- Posts: 26

Hi All

I am switching to this thread because I think this tread is more appropriate for posts dealing with primes. I have previously posted on the "help me" thread.

I am a small time prime hobbyist and have previously posted two "algorithms" that I have developed roughly on my own devices, although I have learned of similar formulations by other researchers/mathematicians, so my stuff might be "copies" or inferior models of what have already been done. I will post my first two "algorithms posted elsewhere on this site for information and comment/criticism!

#1

The 1st algorithm is a variation on the Sieve of Eratosthenes, but actually not a real sieve, but rather a combination of sieve and modulo operations. I discovered recently that there are similar sieves out there (e.g by David Turner of St Andrews University and others -See Wikipedia) so not too sure about the uniqueness of this algorithm therefore. However I did develop the sieve on my own, and I suspect it would be slightly different (and perhaps inferior) to the others. It involves the following; (#1) Take number line of positive integers, 1,2,3....... (#2) strike out all multiples of 2 leaving odd numbers (#3) Identify/mark "3" as a (new) prime number since "3" is not divisible by any positive integer (excluding "1") smaller than itself without leaving a remainder. Calculate square of the newly identified prime (9 in this case). For all odd numbers between 3 and 9 divide by the first prime "2" -all primes less that square root of 9,....nothing to eliminate since 4, 6 & 8 were already eliminated, leaving 5 & 7 as new primes. Now take next prime namely "5". Square of this prime is "25" Now divide all the (odd) numbers remaining on the number line between 9 & 25, by all the identified primes less than "5", namely "2" & "3" . "2" can actually be dropped since all the even numbers had already been eliminated from the number line. This operation eliminates "15,18 & 21", identifying 11,13,17,19 & 23 as primes. (#4) Now do the same for the odd numbers between "25" and the next prime (7=49), dividing with the identified primes less than the square root of (49=7), repeating this operation step by step. The beauty of this operation/algorith is that it identifies primes well ahead of the primes being used in the "sector" being appraised.

#2

My second algorithm is much more curious. We all know that the seemingly random distribution of primes have been a source of amazement to mathematicians for centuries, making it impossible to predict accurately a pattern or the next prime number. However, I have discovered that adding primes together in a particular way (in fact the summing operation of primes seem to produce many solid patterns)-namely consecutive sum of primes produces very REGULAR curves (with coefficients of determination(R^2) of "1" or close to "1"), using the regularity of the obtained curve to "predict" the next prime. This I can do to an accuracy which appear to be an improvement of the estimation provided by the Prime Number Theorum (PNT), and the curve functions anywhere in a series of prime numbers as opposed to the PNT which is more accurate as it approaches infinity. One of the summations is like this (consecutive sum); Add the first two together. Then to the sum add the next prime. To this sum add the next prime number and so on....(p+p), (p+p+p),(p+p+p+p).....This produces a curve of almost perfect slope, whereby it is possible to the predict the NEXT prime by using a trend line or the polynomial equation of the formula. If this curve is true one could potentially predict primes or the location of primes to great numbers. Although I tested the series of consecutive primes in the "Series Encylopedia(OEIS)" it exists, but graphing this series to determine prime numbers has not been done before I think.

I would appreciate further comment.

*Last edited by Gophne (2016-11-15 06:59:16)*

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**iamaditya****Member**- From: Planet Mars
- Registered: 2016-11-15
- Posts: 62

There is also a formula first noticed by Leonhard Euler which proves that the set of primes is endless. The formula is

x²+x+41 is always a prime no. if x is an integer.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 107,776

x²+x+41 is always a prime no. if x is an integer.

That is not always true. Try x = 41.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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iamaditya wrote:

There is also a formula first noticed by Leonhard Euler which proves that the set of primes is endless. The formula is

x²+x+41 is always a prime no. if x is an integer.

This cannot be true: just take x = 41 for instance, which clearly factorises into non-trivial factors. Euler found that this polynomial produces 40 distinct primes for the first 40 values.

In fact, it can be shown that such a polynomial cannot exist.

*Last edited by zetafunc (2016-11-24 08:55:23)*

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