OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..10000
FORMULA
G.f.: sum(n>=1, n*q^(n-1)/(1+q^n) ) * prod(n>=1, 1+q^n ). - Joerg Arndt, Aug 03 2011
a(n) = n * A000009(n). - Vaclav Kotesovec, Sep 25 2016
G.f.: x*f'(x), where f(x) = Product_{k>=1} (1 + x^k). - Vaclav Kotesovec, Nov 21 2016
EXAMPLE
The strict integer partitions of 6 are {(6), (5,1), (4,2), (3,2,1)} with sum 6+5+1+4+2+3+2+1 = 24. - Gus Wiseman, May 09 2019
MAPLE
b:= proc(n, i) option remember; `if`(n=0, [1, 0], `if`(i>n, [0$2],
b(n, i+1)+(p-> p+[0, i*p[1]])(b(n-i, i+1))))
end:
a:= n-> b(n, 1)[2]:
seq(a(n), n=0..80); # Alois P. Heinz, Sep 01 2014
MATHEMATICA
PartitionsQ[ Range[ 60 ] ]Range[ 60 ]
nmax=60; CoefficientList[Series[x*D[Product[1+x^k, {k, 1, nmax}], x], {x, 0, nmax}], x] (* Vaclav Kotesovec, Nov 21 2016 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Wouter Meeussen, Dec 15 2001
STATUS
approved