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%I #4 Feb 14 2018 08:24:00
%S 2,3,5,7,8,11,12,13,17,19,20,23,28,29,31,37,41,43,44,47,52,53,59,61,
%T 67,68,71,73,76,79,83,89,92,97,101,103,107,109,113,116,124,127,131,
%U 137,139,148,149,151,157,163,164,167,172,173,179,181,188,191,193
%N The primes p and products 4*p in increasing order.
%C Conjecture: except for the first term, these are the nonsquares n for which there is a unique pair (x,y) such that x^2 - y^2 = n and x > y >= 0; see A257408.
%H Clark Kimberling, <a href="/A298865/b298865.txt">Table of n, a(n) for n = 1..1000</a>
%t z = 10000; u = Prime[Range[z]]; w = Take[Union[u, 4 u], z]; (* A298865 *)
%t p[n_] := If[MemberQ[u, w[[n]]], 0, 1];
%t t = Table[p[n], {n, 1, z}];
%t Flatten[Position[t, 0]]; (* A298866 *)
%t Flatten[Position[t, 1]]; (* A298867 *)
%Y Cf. A000040, A298866, A298867.
%K nonn,easy
%O 1,1
%A _Clark Kimberling_, Feb 13 2018