OFFSET
0,2
COMMENTS
sigma(n,k) denotes the sum of the k-th power of the divisors of n.
EXAMPLE
a(2) = 1*2*5 + 2*3*3 + 1*5*2.
a(3) = 1*2*28 + 3*4*10 + 3*10*4 + 1*28*2.
a(4) = 1*3*273 + 4*7*73 + 6*21*21 + 4*73*7 + 1*273*3.
a(5) = 1*2*3126 + 5*6*626 + 10*26*126 + 10*126*26 + 5*626*6 + 1*3126*2.
a(6) = 1*4*47450 + 6*12*8052 + 15*50*1394 + 20*252*252 + 15*1394*50 + 6*8052*12 + 1*47450*4.
PROG
(PARI) a(n)=if(n==0, 1, sum(k=0, n, binomial(n, k)*sigma(n, k)*sigma(n, n-k)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Sep 21 2010
STATUS
approved