A205773 G.f. satisfies: A(x) = 1/Product_{n>=1} (1 - 3*x^n*A(x^n)).

1, 3, 21, 156, 1335, 12153, 116778, 1160715, 11848530, 123420648, 1306709841, 14019657771, 152092615971, 1665531792021, 18386262679557, 204393214435791, 2286101345820933, 25708109998131381, 290490321604346535, 3296566844230833750, 37555644504960139647

Offset: 0

Author

Paul D. Hanna, Jan 31 2012

Keywords

• nonn

Examples

			G.f.: A(x) = 1 + 3*x + 21*x^2 + 156*x^3 + 1335*x^4 + 12153*x^5 +...
where
A(x) = 1/((1 - 3*x*A(x)) * (1 - 3*x^2*A(x^2)) * (1 - 3*x^3*A(x^3)) *...).
		

Crossrefs

Cf. A050383, A196192, A205772.

Programs

PARI

{a(n)=local(A=1+x); for(i=1, n, A=1/prod(k=1, n, (1-3*x^k*subst(A, x, x^k+x*O(x^n))))); polcoeff(A, n)}