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

Author

Andrew Howroyd, Sep 03 2019

Keywords

• nonn

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..1000
• Eric Weisstein's World of Mathematics, Maximum Vertex Degree

Crossrefs

Column k=2 of A263293.

A diagonal of A294217.

Cf. A003292, A008619.

Programs

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

Formula

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