A380532 a(n) is the multiplicative order of -5 modulo prime(n); a(3) = 0 for completion.

1, 1, 0, 3, 10, 4, 16, 18, 11, 7, 6, 36, 20, 21, 23, 52, 58, 15, 11, 10, 72, 78, 41, 44, 96, 50, 51, 53, 54, 112, 21, 130, 136, 138, 74, 150, 156, 27, 83, 172, 178, 30, 38, 192, 196, 66, 70, 111, 113, 57, 232, 238, 40, 50, 256, 131, 134, 54, 276, 140

Offset

1,4

Links

Jianing Song, Table of n, a(n) for n = 1..10000

Mathematica

A380532[n_] := If[n == 3, 0, MultiplicativeOrder[-5, Prime[n]]];
Array[A380532, 100] (* Paolo Xausa, Jun 29 2025 *)

Prog

(PARI) a(n, {k=-5}) = my(p = prime(n)); if(k%p==0, 0, znorder(Mod(k, p)))

Crossrefs

Cf. A105877 (primes having primitive root -5).

Cf. bases 2..10: A014664, A062117, A082654, A211241, A211242, A211243, A211244, A211245, A002371.

Cf. bases -2..-10: A337878 (if first term 1), A380482, A380531, this sequence, A380533, A380540, A380541, A380542, A385222.

Sequence in context: A235923 A192028 A384065 * A111229 A100984 A045985

Adjacent sequences: A380529 A380530 A380531 * A380533 A380534 A380535

Keyword

nonn,easy

Author

Jianing Song, Jun 27 2025

Status

approved