A215456 a(n)=(4n-1)!! modulo 2n, n=1,2,...

1, 1, 3, 1, 5, 9, 7, 1, 9, 5, 11, 9, 13, 21, 15, 1, 17, 9, 19, 25, 21, 33, 23, 33, 25, 13, 27, 49, 29, 45, 31, 1, 33, 17, 35, 9, 37, 57, 39, 65, 41, 21, 43, 33, 45, 69, 47, 33, 49, 25, 51, 65, 53, 81, 55, 49, 57, 29, 59, 105, 61, 93, 63, 1, 65, 33, 67, 17, 69

Offset

1,3

Comments

a(n)=1 for n = 2^k. Do all odd integers appear in the sequence?

Note some linear patterns in the graph.

Note that A001147(m) modulo m is 0 for odd m's, hence we here consider only even m's.

Links

Zak Seidov, Table of n, a(n) for n = 1..1000

Formula

a(n)=A001147(2n) modulo 2n, n=1,2,...

Mathematica

Table[Mod[(4n-1)!!, 2n], {n, 70}] (* Harvey P. Dale, Mar 29 2022 *)

Crossrefs

Cf. A001147.

Sequence in context: A221446 A029723 A187370 * A225855 A201751 A202504

Adjacent sequences: A215453 A215454 A215455 * A215457 A215458 A215459

Keyword

nonn

Author

Zak Seidov, Aug 11 2012

Status

approved