A215766 Number of undirected labeled graphs on n nodes with exactly 6 cycle graphs as connected components.

1, 21, 266, 2898, 31899, 375375, 4754200, 64566645, 936889954, 14477748285, 237514188730, 4124517063940, 75606129579493, 1459266319935423, 29585813267243475, 628724462015327265, 13976353234658809071, 324398325664769299713, 7848176443746842027187

Offset: 6

Author

Alois P. Heinz, Aug 23 2012

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 6..170

Crossrefs

Column k=6 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, 6):
seq (a(n), n=6..25);