OFFSET
1,2
COMMENTS
n divides a(n) for n: 1, 3, 4, 8, 12, 24, 28, 84, 88, 144, 264, 432, 440, 476, 1320, ...
Inverse Möbius transform of A064840. - Antti Karttunen, Mar 28 2019
EXAMPLE
a(6) = tau(1)*sigma(1) + tau(2)*sigma(2) + tau(3)*sigma(3) + tau(6)*sigma(6) = (1*1) + (2*3) + (2*4) + (4*12) = 63.
MATHEMATICA
Table[Sum[DivisorSigma[0, k]*DivisorSigma[1, k], {k, Divisors[n]}], {n, 1, 100}] (* Vaclav Kotesovec, Mar 23 2019 *)
PROG
(Magma) [&+[NumberOfDivisors(d) * SumOfDivisors(d): d in Divisors(n)]: n in [1..100]]
(PARI) a(n) = my(d=divisors(n)); sum(i=1, #d, numdiv(d[i])*sigma(d[i])) \\ Felix Fröhlich, Mar 23 2019
(PARI) a(n) = sumdiv(n, d, numdiv(d)*sigma(d)); \\ Michel Marcus, Mar 24 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Mar 23 2019
STATUS
approved