login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A156326 E.g.f.: A(x) = exp( Sum_{n>=1} n^2 * a(n-1)*x^n/n! ) = Sum_{n>=0} a(n)*x^n/n! with a(0) = 1. 6
1, 1, 5, 58, 1181, 36696, 1601497, 92969920, 6908883417, 638746871680, 71860612355981, 9664570175364864, 1531263494465900725, 282321785979644121088, 59935663751282958139425, 14517627118656645274771456, 3980008380007702720451029553, 1226189930561023692489563013120 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..100

FORMULA

a(n) = Sum_{k=1..n} k^2 * C(n-1,k-1)*a(k-1)*a(n-k) for n>0, with a(0)=1.

E.g.f.: A(x) = exp( x*A(x) + x^2*A'(x) ). - Paul D. Hanna, Apr 02 2018

E.g.f.: A(x) = (1/x)*Series_Reversion(x/G(x)) where A(x/G(x)) = G(x) is the e.g.f. of A182962, which satisfies:

. G(x) = exp( x/(1 - x*G'(x)/G(x)) );

. a(n) = [x^n/n!] G(x)^(n+1)/(n+1) for n>=0.

a(n) = A161968(n+1)/(n+1), where L(x) = x*exp(x*d/dx L(x)) is the e.g.f. of A161968. - Paul D. Hanna, Feb 21 2014

a(n) ~ c * n * (n!)^2, where c =  A238223 * exp(1) = 0.592451670452494179138706062417512405957... - Vaclav Kotesovec, Feb 27 2014

EXAMPLE

E.g.f: A(x) = 1 + x + 5*x^2/2! + 58*x^3/3! + 1181*x^4/4! + 36696*x^5/5! + ...

log(A(x)) = x + 2^2*x^2/2! + 3^2*5*x^3/3! + 4^2*58*x^4/4! + 5^2*1181*x^5/5! + ...

MATHEMATICA

nmax = 20; b = ConstantArray[0, nmax+1]; b[[1]] = 1; Do[b[[n+1]] = Sum[k^2 * Binomial[n-1, k-1]*b[[k]]*b[[n-k+1]], {k, 1, n}], {n, 1, nmax}]; b (* Vaclav Kotesovec, Feb 27 2014 *)

PROG

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

(PARI) {a(n)=if(n==0, 1, sum(k=1, n, k^2*binomial(n-1, k-1)*a(k-1)*a(n-k)))}

(PARI) seq(n)={my(a=vector(n+1)); a[1]=1; for(n=1, n, a[1+n] = sum(k=1, n, k^2 * binomial(n-1, k-1)*a[k]*a[1+n-k])); a} \\ Andrew Howroyd, Jan 05 2020

CROSSREFS

Cf. A156325, A156327, A182962, A161968.

Sequence in context: A097631 A130768 A195947 * A001624 A267722 A096476

Adjacent sequences:  A156323 A156324 A156325 * A156327 A156328 A156329

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Feb 08 2009

EXTENSIONS

Terms a(15) and beyond from Andrew Howroyd, Jan 05 2020

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 24 02:48 EST 2020. Contains 332195 sequences. (Running on oeis4.)