A324740 Number of simple graphs on n unlabeled nodes with maximum degree exactly 2.

0, 0, 2, 4, 8, 15, 25, 41, 65, 100, 150, 225, 327, 474, 678, 962, 1348, 1884, 2602, 3581, 4889, 6644, 8968, 12064, 16124, 21476, 28462, 37585, 49407, 64747, 84495, 109936, 142522, 184226, 237350, 304977, 390669, 499169, 636039, 808468, 1024996, 1296573, 1636151

Offset

1,3

Links

Andrew Howroyd, Table of n, a(n) for n = 1..1000

Eric Weisstein's World of Mathematics, Maximum Vertex Degree

Formula

a(n) = A003292(n) - A008619(n).

Prog

(PARI) seq(n) = Vec( (1-x)*(1-x^2)/prod(k=1, n, 1 - x^k + O(x*x^n))^2 - 1/((1-x)*(1-x^2)), -n) \\ Andrew Howroyd, Sep 03 2019

Crossrefs

Column k=2 of A263293.

A diagonal of A294217.

Cf. A003292, A008619.

Sequence in context: A159243 A325840 A347764 * A262146 A089140 A204555

Adjacent sequences: A324737 A324738 A324739 * A324741 A324742 A324743

Keyword

nonn

Author

Andrew Howroyd, Sep 03 2019

Status

approved