A181146 Main diagonal of triangle A181145.

1, 4, 27, 236, 2380, 26216, 306495, 3740572, 47159772, 609924536, 8051939324, 108110654120, 1472276038688, 20292738170064, 282614171731527, 3971576995998588, 56256063139701916, 802448704561822616

Offset

0,2

Comments

Triangle A181145 is formed from the coefficients of the g.f.:

* exp( Sum_{n>=1} [Sum_{k=0..2n} C(2n,k)^2*y^k]*x^n/n ).

Links

Table of n, a(n) for n=0..17.

Example

Triangle A181145 begins:
(1);
1,(4), 1;
1, 12,(27), 12, 1;
1, 24, 134,(236), 134, 24, 1;
1, 40, 410, 1540,(2380), 1540, 410, 40, 1;
1, 60, 975, 6260, 18386,(26216), 18386, 6260, 975, 60, 1; ...
in which this sequence equals the central terms of the rows.

Prog

(PARI) {a(n)=polcoeff(polcoeff(exp(sum(m=1, n, sum(j=0, 2*m, binomial(2*m, j)^2*y^j)*x^m/m)+O(x^(n+1))), n, x), n, y)}

Crossrefs

Cf. A181146.

Sequence in context: A328978 A379192 A185655 * A303559 A161120 A183430

Adjacent sequences: A181143 A181144 A181145 * A181147 A181148 A181149

Keyword

nonn

Author

Paul D. Hanna, Oct 16 2010

Status

approved