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A324740
Number of simple graphs on n unlabeled nodes with maximum degree exactly 2.
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
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.
Sequence in context: A159243 A325840 A347764 * A262146 A089140 A204555
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Sep 03 2019
STATUS
approved