A254231 Product of tribonacci numbers A000073(2) * ... * A000073(n).

1, 1, 2, 8, 56, 728, 17472, 768768, 62270208, 9278260992, 2542243511808, 1281290729951232, 1187756506664792064, 2025124843863470469120, 6350791510355843391160320, 36631365431732504680212725760, 388622155865250142152376807587840

Offset

2,3

Links

Chai Wah Wu, Table of n, a(n) for n = 2..89

Formula

a(n) ~ c * d^(n/2) * r^(n^2/2), where r = A058265 = 1.839286755214161132551852564653286600424178746097592246778758639404203222... is the root of the equation r^3 - r^2 - r - 1 = 0, d = 0.061463687669952618841340986526101395138659648898940720192319213600612851... is the root of the equation -1 + 36*d - 440*d^2 + 1936*d^3 = 0, c = 4.156714772910304733054135311449211887936035199917470476143821433373978333... .

Mathematica

Table[Product[SeriesCoefficient[x^2/(1-x-x^2-x^3), {x, 0, k}], {k, 2, n}], {n, 2, 20}]

Prog

(Python)
A254231_list, a, b, c, d = [1], 0, 0, 1, 1
for _ in range(100):
....a, b, c = b, c, a+b+c
....d *= c
....A254231_list.append(d) # Chai Wah Wu, Jan 27 2015

Crossrefs

Cf. A000073, A003266, A058265, A126772, A135407, A254232.

Sequence in context: A302999 A135079 A084872 * A191713 A191508 A113725

Adjacent sequences: A254228 A254229 A254230 * A254232 A254233 A254234

Keyword

nonn

Author

Vaclav Kotesovec, Jan 27 2015

Status

approved