prime number

**jashansinghal** · October 8th 2009, 06:16 PM

is this possible
if A is a prime number then A + 100 is also prime is A is not a part of the following series
2,5,8,11,14,17,20,23,26............
prove it also

**chisigma** · October 8th 2009, 06:59 PM

Counterexample: $19$ is prime and is not included in the sequence $a_{n} = 2+3n$ , but $119=7\cdot 17$ is not a prime...

Kind regards

$\chi$ $\sigma$

**jashansinghal** · October 9th 2009, 07:16 AM

leaving 19 ,
is there a possibility

**chisigma** · October 9th 2009, 07:38 PM

Further counterexample: $103 \ne 3n-1$ is prime, $203 = 7\cdot 29$ is not a prime...

Kind regards

$\chi$ $\sigma$

**aidan** · October 10th 2009, 03:34 PM

There are over 300 counter examples for numbers less than 10 thousand.

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