A091605 Column 2 of triangle A091602.

1, 0, 2, 2, 3, 4, 7, 8, 12, 15, 21, 26, 35, 43, 57, 70, 89, 109, 138, 167, 208, 251, 309, 371, 452, 539, 652, 775, 929, 1099, 1311, 1543, 1829, 2146, 2529, 2957, 3469, 4040, 4721, 5481, 6377, 7381, 8559, 9875, 11412, 13133, 15128, 17364, 19945, 22833

Offset: 2

Author

Christian G. Bower, Jan 23 2004

Keywords

• nonn

Examples

			a(7) counts these partitions:  511, 331, 322, 3211. - _Clark Kimberling_, Mar 10 2014
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 2..1000

Programs

Mathematica

d[n_] := Select[IntegerPartitions[n], Max[Length /@ Split@#] == 2 &];
t = Table[d[n], {n, 12}]  (* shows partitions *)
u = Table[Length[d[n]], {n, 2, 30}] (* counts partitions *)
(* Clark Kimberling, Mar 10 2014 *)

Formula

a(n) = A000726(n) - A000009(n).