OFFSET
0,3
COMMENTS
a(n)=Sum(k*A116683(n,k), k>=0).
FORMULA
G.f.=2*product(1+x^j,j=1..infinity)*sum((jx^(2j)/(1+x^(2j)), j=1..infinity)).
EXAMPLE
a(9)=34 because in the partitions of 9 into distinct parts, namely, [9],[81],[72],[6,3],[6,2,1],[5,4],[5,3,1] and [4,3,2], the sum of the even parts is 8+2+6+6+2+4+4+2=34.
MAPLE
f:=2*product(1+x^j, j=1..60)*sum((j*x^(2*j)/(1+x^(2*j)), j=1..35)): fser:=series(f, x=0, 55): seq(coeff(fser, x, n), n=0..50);
MATHEMATICA
Map[Total[Select[Flatten[d[#]], EvenQ]] &, -1 + Range[30]] )
(* Peter J. C. Moses, Mar 14 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Feb 22 2006
STATUS
approved