A361405 Number of graphs with loops on 2n unlabeled vertices with n loops.

1, 2, 28, 1408, 580656, 2658827456, 146702084635392, 98485306566812364032, 820443196111261227164076544, 86804253216450161933010414314819072, 119212631345634236227720012129209606659383296, 2166023316743980619769969171366251471253351621687457792

Offset

0,2

Comments

a(n) is the number of bicolored graphs on 2n unlabeled nodes with an equal number of each color. Adjacent vertices may have the same color.

Links

Andrew Howroyd, Table of n, a(n) for n = 0..25

Formula

a(n) = A361404(2*n, n).

Prog

(PARI) a(n) = row(2*n)[n+1] \\ row(n) defined in A361404.

Crossrefs

Central coefficients of A361404.

Cf. A007139.

Sequence in context: A324077 A071220 A063794 * A331839 A238817 A202942

Adjacent sequences: A361402 A361403 A361404 * A361406 A361407 A361408

Keyword

nonn

Author

Andrew Howroyd, Mar 11 2023

Status

approved