OFFSET
1,1
COMMENTS
tau(n) = A000005(n) = the number of divisors of n.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
FORMULA
Logarithmic derivative of A174477.
MATHEMATICA
Table[With[{d=Divisors[n]}, Total[d 2^(n/d) DivisorSigma[0, d]]], {n, 40}] (* Harvey P. Dale, Nov 13 2021 *)
PROG
(PARI) {a(n)=sumdiv(n, d, d*2^(n/d)*sigma(d, 0))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Apr 04 2010
STATUS
approved