A099168 a(n) = 3^n * 5^binomial(n,2).

1, 3, 45, 3375, 1265625, 2373046875, 22247314453125, 1042842864990234375, 244416296482086181640625, 286425347439944744110107421875, 1678273520155926235020160675048828125

Offset

0,2

Links

Table of n, a(n) for n=0..10.

Theresia Eisenkölbl, 2-Enumerations of halved alternating sign matrices, Séminaire Lotharingien de Combinatoire, B46c (2001), 11 pp.

Formula

0 = a(n)*a(n+2) - 5*a(n+1)^2 for all n in Z. - Michael Somos, Dec 03 2016

Example

G.f. = 1 + 3*x + 45*x^2 + 3375*x^3 + 1265625*x^4 + 2373046875*x^5 + ...

Mathematica

Table[3^n 5^Binomial[n, 2], {n, 0, 10}] (* Harvey P. Dale, Dec 17 2020 *)

Prog

(PARI) a(n) = 3^n * 5^binomial(n, 2); \\ Michel Marcus, Dec 02 2016

Crossrefs

Cf. A002416.

Sequence in context: A027637 A228903 A198952 * A227379 A004105 A060336

Adjacent sequences: A099165 A099166 A099167 * A099169 A099170 A099171

Keyword

nonn

Author

Ralf Stephan, Oct 09 2004

Status

approved