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%I #4 Dec 05 2013 19:56:31
%S 1,3,9,0,7,26,32,35,29,11,109,31,95,43,394,67,127,23,55,224,107,265,
%T 237,92,158,386,233,989,401,1229,714,197,380,384,541,142,179,376,908,
%U 149,723,963,169,2187,909,919,519,360,674,1376,636,643,2468,1284,504,781
%N a(n) = index of the first occurrence of n in A087565, or 0 if n is not a term of A087565.
%C Smallest k such that n is the smallest number for which k*(k+1)*(k+2)...(k+n) + 1 is prime.
%C a(3) = 0 since 3 is not a term of A087565 because k*(k+1)*(k+2)*(k+3) + 1 is a square for every k.
%e a(1) = 3 since 1+1 is prime, 2+1 is prime, 3+1 is composite, 3*(3+1)+1 = 13 is prime.
%o (PARI) {p=55; a=2500; v=vector(p+1); for(n=1,a,k=0; m=n; while(!isprime(m+1,1)&& k<=p+1,k++; m=m*(n+k)); if(k<=p,if(v[k+1]<1,v[k+1]=n))); for(j=1,p+1,print1(v[j],","))}
%Y Cf. A087564, A087565.
%K nonn
%O 0,2
%A _Amarnath Murthy_, Sep 15 2003
%E Edited and extended by _Klaus Brockhaus_, Sep 20 2003