A057756 Least nonnegative square root of -1 mod n for n in A008784.

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, 11, 57, 47, 37, 12, 27, 44, 28, 70, 13, 80, 55, 19, 43, 81, 75, 14, 91, 32, 33, 21, 15, 107, 89, 64, 57, 16, 23, 82, 37, 60, 53, 38, 17, 138, 105

Offset: 1

Author

N. J. A. Sloane, Nov 01 2000

Keywords

• nonn
• easy
• nice

Links

• T. D. Noe, Table of n, a(n) for n=1..1000

Crossrefs

Cf. A008784.

Programs

Mathematica

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 *)

Extensions

Corrected by T. D. Noe, Apr 19 2007 [The errors were caused by the faulty Maple command "mroot"]