%I #18 Feb 17 2018 18:33:56
%S 1,4,11,2,37,56,11,106,21,172,3,42,301,60,407,22,93,596,119,742,9,4,
%T 991,42,1177,1276,255,62,37,1712,1831,366,2081,416,2347,2486,5,60,555,
%U 3082,153,12,3571,714,189,56,127,4466,893,120,5051,1010,97,176,403,6,1221,332,127,14,7261,24,539,1550,93
%N a(n) = min(x : x^2 + n^2 = 0 mod (x+n-1)).
%F a(n) = 2*n^2 - 3*n+2 for n=1, 2, 3, 5, 6, 8, 10, 13, 15, 18, 20, 23, 25, 26, 30, 31, 33, 35, 36, 40, 43, ...
%t a[n_] := For[x = 1, True, x++, If[Mod[x^2+n^2, x+n-1] == 0, Return[x]]]; Array[a, 40] (* _Jean-François Alcover_, Feb 17 2018 *)
%o (PARI) a(n) = {my(k=1); while((k^2+n^2)%(k+n-1) != 0, k++); k;} \\ _Altug Alkan_, Feb 17 2018
%K nonn
%O 1,2
%A _Benoit Cloitre_, Jan 01 2002
%E a(28) corrected by _Altug Alkan_, Feb 17 2018