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%I #15 Apr 17 2022 20:37:04
%S 0,1,2,3,5,4,7,5,12,13,6,9,7,23,17,11,8,27,31,9,13,34,22,10,23,33,15,
%T 11,57,47,37,12,27,44,28,70,13,80,55,19,43,81,75,14,91,32,33,21,15,
%U 107,89,64,57,16,23,82,37,60,53,38,17,138,105
%N Least nonnegative square root of -1 mod n for n in A008784.
%H T. D. Noe, <a href="/A057756/b057756.txt">Table of n, a(n) for n=1..1000</a>
%t A008784 = Select[ Range[300], And @@ (Mod[#, 4] == 1 & ) /@ (fi = FactorInteger[#]; If[ fi[[1]] == {2, 1}, Rest[ fi[[All, 1]]], fi[[All, 1]]])& ]; a[n_] := Min[r /. {ToRules[ Reduce[ Mod[r^2 + 1, A008784[[n]]] == 0, r, Integers] /. C[1] -> 0]}]; a[1] = 0; Table[a[n], {n, 1, 63}] (* _Jean-François Alcover_, Sep 19 2012 *)
%Y Cf. A008784.
%K nonn,easy,nice
%O 1,3
%A _N. J. A. Sloane_, Nov 01 2000
%E Corrected by _T. D. Noe_, Apr 19 2007 [The errors were caused by the faulty Maple command "mroot"]
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