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%I #39 Nov 21 2014 21:27:15
%S 3,2,2,2,2,2,2,2,2,2,2,2,2,2,2,3,2,2,3,2,2,2,2,2,2,5,2,2,2,3,3,2,2,2,
%T 2,5,2,2,2,3,2,2,2,2,2,2,2,2,2,2,3,3,3,2,2,2,3,2,2,2,47,3,3,2,2,2,2,2,
%U 2,2,11,2,23,17,2,2,2,2,2,3
%N Smallest prime Q such that there is a prime R such that Q*(R+1)+1 or Q*(R+1)-1 or Q*(R-1)+1 or Q*(R-1)-1 is prime(n), or 0 if no such prime Q exists.
%C The first prime prime(n) with no solution is prime(1300)=10657.
%C There are 43 terms 0 within the first 10000 primes.
%H Pierre CAMI, <a href="/A248743/b248743.txt">Table of n, a(n) for n = 1..10000</a>
%e 2=3*(2-1)-1, so a(1)=3.
%e 3=2*(3-1)-1, so a(2)=2.
%e 5=2*(2+1)-1=2*(3-1)+1, so a(3)=2.
%e 7=2*(2+1)+1=2*(3+1)-1=2*(5-1)-1, so a(4)=2.
%o (PARI) a(p) = {if (p == 2, return (3)); forprime (q=2, p, if (!((p-1) % q) && (isprime((p-1)/q+1) || isprime((p-1)/q-1)), return (q)); if (!((p+1) % q) && (isprime((p+1)/q+1) || isprime((p+1)/q-1)), return (q)););} \\ to be used with a forprime loop; _Michel Marcus_, Oct 28 2014
%K nonn
%O 1,1
%A _Pierre CAMI_, Oct 13 2014
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