A215764 Number of undirected labeled graphs on n nodes with exactly 4 cycle graphs as connected components.

1, 10, 65, 420, 3157, 27342, 264925, 2831455, 33077539, 419262987, 5730379473, 84009491475, 1315019717433, 21890336017248, 386143234692768, 7195289865439824, 141228388872794736, 2912462945497687680, 62959048637195335680, 1423638554827333204800

Offset: 4

Author

Alois P. Heinz, Aug 23 2012

Keywords

• nonn

Examples

			a(4) = 1:  o1.2o
.          .....
.          o3.4o
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 4..175

Crossrefs

Column k=4 of A215771.

Programs

Maple

T:= proc(n, k) option remember; `if`(k<0 or k>n, 0, `if`(n=0, 1,
      add(binomial(n-1, i)*T(n-1-i, k-1)*ceil(i!/2), i=0..n-k)))
    end:
a:= n-> T(n, 4):
seq (a(n), n=4..25);