A143768 E.g.f. satisfies A(x) = exp(x + x^2*A(x)^2).

1, 1, 3, 19, 169, 2041, 30811, 560827, 11957905, 292399345, 8069068531, 248093713891, 8411093625529, 311750189715433, 12541478207183563, 544268121894899851, 25345579186001847841, 1260715969618060192225

Offset

0,3

Links

Seiichi Manyama, Table of n, a(n) for n = 0..378

Formula

Expansion of [LambertW(-2*x^2*exp(2x))/(-2*x^2)]^(1/2).

E.g.f.: A(x) = Sum_{m>=0} (2n+1)^(n-1) * exp((2n+1)*x) * x^(2n)/n! .

From Paul D. Hanna, Jul 11 2009: (Start)

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

Let A(x)^m = Sum_{n>=0} a(n,m)*x^n/n!, then

a(n,m) = n! * Sum_{k=0..n} C(k,n-k) * m*(2*(n-k)+m)^(k-1)/k!.

...

If log(A(x)) = Sum_{n>=1} L(n)*x^n/n!, then

L(n) = n! * Sum_{k=0..n} (2*(n-k))^(k-1)/k! * C(k,n-k). (End)

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

Example

E.g.f.: A(x) = 1 + x + 3*x^2/2! + 19*x^3/3! + 169*x^4/4! + 2041*x^5/5! + ...
A(x)^2 = 1 + 2*x + 8*x^2/2! + 56*x^3/3! + 544*x^4/4! + 6912*x^5/5! + ...
log(A(x)) = x + x^2 + 2*x^3 + 8*x^4/2! + 56*x^5/3! + 544*x^6/4! + ...

Mathematica

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

Prog

(PARI) {a(n)=local(A=1+x*O(x^n)); for(i=0, n, A=exp(x+x^2*A^2)); (n+0)!*polcoeff(A, n)}
(PARI) {a(n)=local(A=sum(m=0, n, 1*(2*m+1)^(m-1)*(x^2)^m*exp((2*m+1)*x+x*O(x^n))/m!)); n!*polcoeff(A, n)}
(PARI) a(n, m=1)=n!*sum(k=0, n, m*(2*(n-k)+m)^(k-1)/k!*binomial(k, n-k)) \\ Paul D. Hanna, Jul 11 2009

Crossrefs

Cf. A047974, A088695, A125500 (variant).

Sequence in context: A085295 A094956 A080894 * A256493 A353256 A275283

Adjacent sequences: A143765 A143766 A143767 * A143769 A143770 A143771

Keyword

nonn

Author

Paul D. Hanna, Aug 31 2008

Status

approved