A215987 Number of simple unlabeled graphs on n nodes with exactly 7 connected components that are trees or cycles.

1, 1, 3, 6, 13, 26, 56, 115, 246, 530, 1166, 2613, 5982, 13940, 33073, 79760, 195109, 483615, 1212485, 3071358, 7850690, 20231286, 52513864, 137202595, 360578812, 952705531, 2529454122, 6745724961, 18063628118, 48553319703, 130962595786, 354390168855

Offset: 7

Author

Alois P. Heinz, Aug 29 2012

Keywords

• nonn

Examples

			a(9) = 3: .o-o o o o.  .o-o o o o.  .o o o o o.
          .|/       .  .|        .  .| |      .
          .o o o o  .  .o o o o  .  .o o o o  .
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 7..650

Crossrefs

Column k=7 of A215977.

The labeled version is A215857.

Programs

Maple

with(numtheory):
b:= proc(n) option remember; local d, j; `if`(n<=1, n,
      (add(add(d*b(d), d=divisors(j)) *b(n-j), j=1..n-1))/(n-1))
    end:
g:= proc(n) option remember; local k; `if`(n>2, 1, 0)+ b(n)-
      (add(b(k)*b(n-k), k=0..n) -`if`(irem(n, 2)=0, b(n/2), 0))/2
    end:
p:= proc(n, i, t) option remember; `if`(n p(n, n, 7):
seq(a(n), n=7..50);