cp's OEIS Frontend

A223705 Least number k such that prime(n) is the largest divisor of k^2 + 1, or 0 if there is no such k.

%I A223705 #3 Apr 03 2013 22:51:51
%S A223705 1,0,2,0,0,5,4,0,0,12,0,6,9,0,0,23,0,11,0,0,27,0,0,34,22,10,0,0,33,15,
%T A223705 0,0,37,0,44,0,28,0,0,80,0,19,0,81,14,0,0,0,0,107,89,0,64,0,16,0,82,0,
%U A223705 60,53,0,138,0,0,25,114,0,148,0,136,42,0,0,104,0,0
%N A223705 Least number k such that prime(n) is the largest divisor of k^2 + 1, or 0 if there is no such k.
%C A223705 Note that a(n) = 0 for prime(n) = 3 (mod 4). If the zeros are removed, A002314 (with 1 prepended) and A177979 are produced.
%t A223705 nn = 100; t = Table[0, {nn}]; Do[If[Mod[Prime[n], 4] == 3, t[[n]] = -1], {n, nn}]; n = 0; While[Times @@ t == 0, n++; s = FactorInteger[n^2 + 1][[-1, 1]]; p = PrimePi[s]; If[p <= nn && t[[p]] == 0, t[[p]] = n]]; Do[If[Mod[Prime[n], 4] == 3, t[[n]] = 0], {n, nn}]; t
%Y A223705 Cf. A223701-A223707 (related sequences).
%K A223705 nonn
%O A223705 1,3
%A A223705 _T. D. Noe_, Apr 03 2013