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%I #18 Aug 17 2014 02:57:27
%S 0,0,0,1,1,1,0,0,1,0,1,1,1,0,1,0,1,1,0,0,1,0,1,0,1,0,0,0,1,1,0,0,0,0,
%T 2,0,2,0,1,0,0,1,1,0,1,0,2,0,0,0,0,0,1,0,1,0,0,0,0,1,0,0,0,0,2,0,1,0,
%U 1,0,0,1,1,0,0,0,2,0,0,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,1,0
%N Number of k >= 1 that make n + k! and n - k! both prime.
%C 0 <= a(n) <= min{A125162(n), A175940(n)}.
%C a(n) < A020639(n). - _Robert Israel_, Aug 12 2014
%H Jens Kruse Andersen, <a href="/A242041/b242041.txt">Table of n, a(n) for n = 1..10000</a>
%p a:= n -> nops(select(k -> isprime(n+k!) and isprime(n-k!),
%p [$1 ..min(numtheory:-factorset(n))-1])):
%p 0, seq(a(n),n=2..100); # _Robert Israel_, Aug 12 2014
%o (PARI)
%o a(n)=c=0;for(k=1,n,if(ispseudoprime(n+k!)&&ispseudoprime(n-k!),c++));return(c)
%o vector(100,n,a(n))
%Y Cf. A020639, A125162, A175940.
%K nonn
%O 1,35
%A _Derek Orr_, Aug 12 2014