A120639 - OEIS

%I #6 Oct 01 2013 17:58:26

%S 2,3,5,7,11,13,17,37,41,43,53,67,71,73,79,83,97,127,131,137,139,163,

%T 173,193,197,199,227,263,277,281,293,307,373,383,409,431,433,467,487,

%U 499,503,521,563,577,587,593,617,619,673,677,683,701,709,727,739,743,797

%N Primes such that their quadruple is 1 away from a prime number.

%C This sequence is a variation of the sequence in the reference. However, this sequence should have an infinite number of terms. k=2 in the PARI code.

%D R. Crandall and C. Pomerance, Prime Numbers A Computational Perspective, Springer Verlag 2002, p. 49, exercise 1.18.

%H Harvey P. Dale, <a href="/A120639/b120639.txt">Table of n, a(n) for n = 1..1000</a>

%e 17*4 = 68, one away from 67 which is prime.

%t Select[Prime[Range[200]],Or@@PrimeQ[4#+{1,-1}]&] (* _Harvey P. Dale_, Feb 18 2013 *)

%o (PARI) primepm2(n,k) = \k = number of iterations,k = factor { local(x,p1,p2,f1,f2,r); if(k%2,r=2,r=1); for(x=1,n, p1=prime(x); p2=prime(x+1); if(isprime(p1*k+r)||isprime(p1*k-r), print1(p1",") ) ) }

%K easy,nonn

%O 1,1

%A _Cino Hilliard_, Aug 17 2006