A120637 - OEIS

%I #10 Oct 01 2013 17:58:26

%S 3,5,7,11,13,17,19,23,29,37,43,47,53,59,61,67,71,79,83,89,97,103,113,

%T 127,137,139,149,163,167,173,181,191,193,197,199,211,227,233,239,251,

%U 257,263,269,271,277,293,307,313,317,331,337,347,349,353,367,373,383

%N Primes such that their triple is 2 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.

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

%F Union of A023208 and A088878.

%e 19 is a prime and 19*3 = 57 which is two away from 59 which is prime.

%e 31 is not in the table because 31*3 = 93 which is 2 away from 91 and 95, both not prime.

%t Select[Prime[Range[200]],PrimeQ[3#+2]||PrimeQ[3#-2]&] (* _Harvey P. Dale_, Aug 10 2011 *)

%o (PARI) primepm2(n,k) { 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",") ) ) }

%Y Cf. A125272.

%K easy,nonn

%O 1,1

%A _Cino Hilliard_, Aug 17 2006