A222077 O.g.f.: Sum_{n>=0} n^n*(n+3)^n * exp(-n*(n+3)*x) * x^n / n!.

1, 4, 34, 504, 10572, 285408, 9419440, 367571200, 16562241744, 846509123520, 48401180913824, 3061687935718272, 212316590908782336, 16018267935253721088, 1306322033185206970368, 114519518777575592865792, 10740222055670467832259840, 1073051903942317493993088000

Offset

0,2

Links

G. C. Greubel, Table of n, a(n) for n = 0..340

Formula

a(n) = 1/n! * [x^n] Sum_{k>=0} k^k*(k+3)^k * x^k / (1 + k*(k+3)*x)^(k+1).

a(n) = 1/n! * Sum_{k=0..n} (-1)^(n-k)*binomial(n,k) * k^n * (k+3)^n.

a(n) ~ n^n * 2^(2*n+1) / (sqrt(Pi*(1-c)*n) * exp(n) * (2-c)^n * c^(n+3/2)), where c = -LambertW(-2*exp(-2)) = 0.4063757399599599... . - Vaclav Kotesovec, May 22 2014

Example

O.g.f.: A(x) = 1 + 4*x + 34*x^2 + 504*x^3 + 10572*x^4 + 285408*x^5 +...
where
A(x) = 1 + 4*x*exp(-4*x) + 10^2*exp(-10*x)*x^2/2! + 18^3*exp(-18*x)*x^3/3! + 28^4*exp(-28*x)*x^4/4! + 40^5*exp(-40*x)*x^5/5! +...
is a power series in x with integer coefficients.

Mathematica

Flatten[{1, Table[Sum[Binomial[n, j] * 3^(n-j) * StirlingS2[n+j, n], {j, 0, n}], {n, 1, 20}]}] (* Vaclav Kotesovec, May 22 2014 *)

Prog

(PARI) {a(n)=polcoeff(sum(m=0, n, m^m*(m+3)^m*x^m*exp(-m*(m+3)*x+x*O(x^n))/m!), n)}
for(n=0, 20, print1(a(n), ", "))
(PARI) {a(n)=(1/n!)*polcoeff(sum(k=0, n, k^k*(k+3)^k*x^k/(1+k*(k+3)*x +x*O(x^n))^(k+1)), n)}
for(n=0, 20, print1(a(n), ", "))
(PARI) {a(n)=1/n!*sum(k=0, n, (-1)^(n-k)*binomial(n, k)*k^n*(k+3)^n)}
for(n=0, 20, print1(a(n), ", "))

Crossrefs

Cf. A217902, A217900, A222076, A222078, A222079.

Sequence in context: A198717 A198908 A207864 * A081972 A158961 A134354

Adjacent sequences: A222074 A222075 A222076 * A222078 A222079 A222080

Keyword

nonn

Author

Paul D. Hanna, Feb 24 2013

Status

approved