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

Author

Andrew Howroyd, Mar 11 2023

Keywords

• nonn

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

Crossrefs

Central coefficients of A361404.

Cf. A007139.

Programs

PARI

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

Formula

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