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**Primenumbers****Member**- Registered: 2013-01-22
- Posts: 37

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.

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,673

Hi Primenumbers

Welcome to the forum!

Here lies the reader who will never open this book. He is forever dead.

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

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 90,798

Hi Primenumbers;

Welcome to the forum!

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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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: 57

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: 90,798

Hi kerr;

is the prime number.**In mathematics, you don't understand things. You just get used to them.**

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**Primenumbers****Member**- Registered: 2013-01-22
- Posts: 37

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.

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**Primenumbers****Member**- Registered: 2013-01-22
- Posts: 37

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.

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