A058737 Main diagonal of A058735.

1, 1, 3, 7, 20, 55, 162, 477, 1450, 4446, 13858, 43589, 138515, 443487, 1430261, 4640312, 15137893, 49620637, 163360133, 539904503, 1790699059, 5958280016, 19883532941, 66532519727, 223177199775, 750340752081, 2528058240115

Offset: 2

Author

N. J. A. Sloane, Jan 01 2001

Keywords

• nonn

Comments

Also the number of unlabeled cographs on n nodes with two components. - Vladeta Jovovic, May 07 2005

References

• J. Riordan, The blossoming of Schroeder's fourth problem, Acta Math., 137 (1976), 1-16.

Links

• Eric Weisstein's World of Mathematics, Cograph
• Index entries for sequences related to rooted trees

Crossrefs

Cf. A000669, A058735, A106240.

Formula

G.f.: A(x) = (B(x)^2 + B(x^2))/2, where B(x) = g.f. for A000669. - Vladeta Jovovic, May 07 2005

Extensions

More terms from Vladeta Jovovic, May 07 2005