A216669 Total number of parts in all partitions of n into 2 sizes of parts (A002133).

2, 5, 14, 20, 39, 52, 74, 102, 134, 158, 208, 259, 284, 361, 409, 488, 538, 634, 678, 838, 857, 1006, 1038, 1270, 1264, 1495, 1500, 1776, 1761, 2084, 2062, 2443, 2300, 2795, 2680, 3194, 3076, 3544, 3403, 4080, 3804, 4518, 4282, 5037, 4673, 5626, 5127, 6088

Offset

3,1

Comments

Also column k=2 of A255768. - Omar E. Pol, Jul 26 2015

Links

Alois P. Heinz, Table of n, a(n) for n = 3..1000

Formula

a(n) = Sum_{k=2..n-1} k * A216665(n,k).

Mathematica

nn=40; ss=Sum[Sum[y^2 x^(i+j)/(1-y x^i)/(1-y x^j), {j, 1, i-1}], {i, 1, nn}]; CoefficientList[Series[D[ss, y]/.y->1, {x, 0, nn}], x]

Crossrefs

Cf. A002133, A216665, A255768.

Sequence in context: A089410 A118670 A228958 * A015633 A176191 A265248

Adjacent sequences: A216666 A216667 A216668 * A216670 A216671 A216672

Keyword

nonn

Author

Geoffrey Critzer, Sep 13 2012

Status

approved