A242040 - OEIS

%I #14 Aug 17 2014 02:50:59

%S 4,5,6,9,11,12,13,15,17,18,21,23,25,29,30,35,37,39,42,43,45,47,53,55,

%T 60,65,67,69,72,73,77,81,83,85,95,99,102,103,105,107,108,111,113,125,

%U 127,129,131,133,137,138,143,145,149,150,151,155,157,161,163,165,173,175,180,185,187

%N Numbers n such that n + k! and n - k! are both prime for some k.

%C Subsequence of the complement of (A239321 union A125163).

%H Jens Kruse Andersen, <a href="/A242040/b242040.txt">Table of n, a(n) for n = 1..10000</a>

%e 5 + 2! = 7 and 5 - 2! = 3 are both prime. Thus 5 is a member of this sequence.

%o (PARI)

%o a(n)=for(k=1,n,if(ispseudoprime(n+k!)&&ispseudoprime(n-k!),return(k)))

%o n=1;while(n<500,if(a(n),print1(n,", "));n++)

%Y Cf. A239321, A125163, A241425, A245716.

%K nonn

%O 1,1

%A _Derek Orr_, Aug 12 2014