A324591 - OEIS

A324591

E.g.f.: exp(2 * (x + x^2 / 2 + x^3 / 3)).

1, 2, 6, 24, 108, 552, 3144, 19392, 129168, 920736, 6958944, 55582848, 466824384, 4104798336, 37688879232, 360236187648, 3575154053376, 36768528142848, 391060780180992, 4293782854170624, 48597548604926976, 566152604314232832, 6780179847538722816, 83375209195856216064

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OFFSET

0,2

LINKS

Table of n, a(n) for n=0..23.

FORMULA

D-finite recurrence: a(n) = 2 * (a(n-1) + (n-1) * a(n-2) + (n-1) * (n-2) * a(n-3)).

a(n) = Sum_{k=0..n} binomial(n,k) * A057693(k) * A057693(n-k).

MATHEMATICA

nmax = 23; CoefficientList[Series[Exp[2 (x + x^2/2 + x^3/3)], {x, 0, nmax}], x] Range[0, nmax]!

a[0] = 1; a[1] = 2; a[2] = 6; a[n_] := a[n] = 2 (a[n - 1] + (n - 1) a[n - 2] + (n - 1) (n - 2) a[n - 3]); Table[a[n], {n, 0, 23}]

PROG

(PARI) my(x='x+O('x^30)); Vec(serlaplace(exp(2*(x + x^2/2 + x^3/3)))) \\ Michel Marcus, Nov 21 2020

CROSSREFS

Cf. A000898, A057693.

Sequence in context: A277248 A189840 A189255 * A338987 A174076 A230695

Adjacent sequences: A324588 A324589 A324590 * A324592 A324593 A324594

KEYWORD

nonn

AUTHOR

Ilya Gutkovskiy, Nov 20 2020

STATUS

approved