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A003560 Least number m such that 4^m = +- 1 mod 4n + 1. 1
1, 1, 3, 3, 2, 3, 5, 7, 5, 9, 5, 6, 21, 13, 9, 15, 3, 11, 9, 15, 27, 4, 11, 5, 12, 25, 6, 9, 7, 6, 55, 25, 7, 9, 17, 23, 7, 37, 12, 13, 33, 10, 39, 43, 29, 45, 9, 9, 24, 49, 33, 5, 45, 35, 15, 12, 30, 19, 29, 39, 6 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..5000

FORMULA

a(n) <= A003573(n). - Michel Marcus, Jun 10 2019

MATHEMATICA

Table[Module[{m=1}, While[PowerMod[4, m, 4 n + 1]!=1 && PowerMod[4, m, 4 n + 1]!=4 n, m++]; m], {n, 0, 70}] (* Vincenzo Librandi, Jun 10 2019 *)

PROG

(PARI) a(n) = {my(m=1); while (((mm=Mod(4, 4*n+1)^m) != 1) && (mm != 4*n), m++); m; } \\ Michel Marcus, Jun 10 2019

CROSSREFS

Cf. A003573.

Sequence in context: A261735 A129309 A268931 * A262212 A123676 A326814

Adjacent sequences:  A003557 A003558 A003559 * A003561 A003562 A003563

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified May 12 05:30 EDT 2021. Contains 343812 sequences. (Running on oeis4.)