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

2,3

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

Table of n, a(n) for n=2..28.

Eric Weisstein's World of Mathematics, Cograph

Index entries for sequences related to rooted trees

Formula

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

Crossrefs

Cf. A000669, A058735, A106240.

Sequence in context: A000227 A327993 A245891 * A274478 A238124 A129429

Adjacent sequences: A058734 A058735 A058736 * A058738 A058739 A058740

Keyword

nonn

Author

N. J. A. Sloane, Jan 01 2001

Extensions

More terms from Vladeta Jovovic, May 07 2005

Status

approved