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A196555 O.g.f.: Sum_{n>=0} 2*(n+2)^(n-1) * x^n / Product_{k=1..n} (1+k*x). 3
1, 2, 6, 28, 186, 1614, 17332, 222254, 3317326, 56532264, 1083571422, 23081180918, 541047188936, 13843339479298, 383952455939662, 11475711580482268, 367729128426998450, 12577206203908139494, 457341567152354085700, 17619050162270848917366 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..19.

FORMULA

E.g.f.: exp(-2*LambertW(exp(-x)-1)).

a(n) = Sum_{k=0..n} (-1)^(n-k)*Stirling2(n, k)*2*(k+2)^(k-1).

a(n) = Sum_{k=0..n} C(n,k)*A058864(n-k)*A058864(k); exponential convolution of A058864, which is the number of labeled chordal graphs (connected or not) on n nodes with no induced path P_4.

a(n) ~ 2*sqrt(exp(1)-1) * n^(n-1) / (exp(n-2) * (1-log(exp(1)-1))^(n-1/2)). - Vaclav Kotesovec, Jul 09 2013

EXAMPLE

O.g.f.: A(x) = 1 + 2*x + 6*x^2 + 28*x^3 + 186*x^4 + 1614*x^5 +...

where the o.g.f. is given by:

A(x) = 1 + 2*3^0*x/(1+x) + 2*4^1*x^2/((1+x)*(1+2*x)) + 2*5^2*x^3/((1+x)*(1+2*x)*(1+3*x)) + 2*6^3*x^4/((1+x)*(1+2*x)*(1+3*x)*(1+4*x)) +...

E.g.f.: A(x) = 1 + 2*x + 6*x^2/2! + 28*x^3/3! + 186*x^4/4! + 1614*x^5/5! +...

where the e.g.f. is given by:

A(x)^(1/2) = 1 + x + 2*x^2/2! + 8*x^3/3! + 49*x^4/4! + 402*x^5/5! + 4144*x^6/6! +...+ A058864(n)*x^n/n! +...

MATHEMATICA

CoefficientList[Series[E^(-2*LambertW[E^(-x)-1]), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Jul 09 2013 *)

PROG

(PARI) {a(n)=polcoeff(sum(m=0, n, 2*(m+2)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)}

(PARI) {A058864(n)=polcoeff(sum(m=0, n, (m+1)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)}

{a(n) = sum(k=0, n, binomial(n, k)*A058864(n-k)*A058864(k))}

(PARI) {Stirling2(n, k)=if(k<0|k>n, 0, sum(i=0, k, (-1)^i*binomial(k, i)/k!*(k-i)^n))}

{a(n)=sum(k=0, n, (-1)^(n-k)*Stirling2(n, k)*2*(k+2)^(k-1))}

CROSSREFS

Cf. A058864, A196556, A196557.

Sequence in context: A100526 A200560 A303344 * A084262 A231621 A084870

Adjacent sequences:  A196552 A196553 A196554 * A196556 A196557 A196558

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Oct 03 2011

STATUS

approved

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Last modified June 15 00:00 EDT 2021. Contains 345041 sequences. (Running on oeis4.)