A240664 Least k such that 9^k == -1 (mod prime(n)), or 0 if no such k exists.

1, 0, 1, 0, 0, 0, 4, 0, 0, 7, 0, 0, 2, 0, 0, 13, 0, 0, 0, 0, 3, 0, 0, 22, 12, 25, 0, 0, 0, 28, 0, 0, 34, 0, 37, 0, 0, 0, 0, 43, 0, 0, 0, 4, 49, 0, 0, 0, 0, 0, 58, 0, 30, 0, 64, 0, 67, 0, 0, 70, 0, 73, 0, 0, 0, 79, 0, 42, 0, 0, 88, 0, 0, 0, 0, 0, 97, 0, 100, 51, 0

Offset

1,7

Comments

The least k, if it exists, such that prime(n) divides 9^k + 1.

Links

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

Formula

a(1) = 1; for n > 1, a(n) = A211245(n)/2 if A211245(n) is even, otherwise 0.

Mathematica

Table[p = Prime[n]; s = Select[Range[p/2], PowerMod[9, #, p] == p - 1 &, 1]; If[s == {}, 0, s[[1]]], {n, 100}]

Crossrefs

Cf. A211245 (order of 9 mod prime(n)).

Sequence in context: A063730 A355945 A131431 * A255328 A321433 A016678

Adjacent sequences: A240661 A240662 A240663 * A240665 A240666 A240667

Keyword

nonn

Author

T. D. Noe, Apr 14 2014

Status

approved