A346889 Expansion of e.g.f. 1 / (1 - x^3 * exp(x) / 3!).

1, 0, 0, 1, 4, 10, 40, 315, 2296, 15204, 117720, 1127445, 11531740, 120909646, 1370809804, 17111895255, 227853866800, 3182209445640, 47003318806896, 737325061500009, 12187616610231540, 210930852047426770, 3821604062633503300, 72479758506840597451

Offset

0,5

Links

Seiichi Manyama, Table of n, a(n) for n = 0..464

Formula

a(0) = 1; a(n) = Sum_{k=1..n} binomial(n,k) * binomial(k,3) * a(n-k).

a(n) ~ n! / ((1 + LambertW(2^(1/3)/3^(2/3))) * 3^(n+1) * LambertW(2^(1/3)/3^(2/3))^n). - Vaclav Kotesovec, Aug 08 2021

a(n) = n! * Sum_{k=0..floor(n/3)} k^(n-3*k)/(6^k * (n-3*k)!). - Seiichi Manyama, May 13 2022

Mathematica

nmax = 23; CoefficientList[Series[1/(1 - x^3 Exp[x]/3!), {x, 0, nmax}], x] Range[0, nmax]!
a[0] = 1; a[n_] := a[n] = Sum[Binomial[n, k] Binomial[k, 3] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 23}]

Prog

(PARI) my(x='x+O('x^25)); Vec(serlaplace(1/(1-x^3*exp(x)/3!))) \\ Michel Marcus, Aug 06 2021
(PARI) a(n) = n!*sum(k=0, n\3, k^(n-3*k)/(6^k*(n-3*k)!)); \\ Seiichi Manyama, May 13 2022

Crossrefs

Column k=3 of A351703.

Cf. A006153, A346888, A346890, A346893.

Cf. A000292, A145453, A353999.

Sequence in context: A370997 A355993 A220817 * A114918 A224488 A149213

Adjacent sequences: A346886 A346887 A346888 * A346890 A346891 A346892

Keyword

nonn

Author

Ilya Gutkovskiy, Aug 06 2021

Status

approved