login
A216669
Total number of parts in all partitions of n into 2 sizes of parts (A002133).
2
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
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
KEYWORD
nonn
AUTHOR
Geoffrey Critzer, Sep 13 2012
STATUS
approved