OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = Sum_{d|n, gcd(d, n/d) = 1} usigma(d), where usigma = A034448. - Ilya Gutkovskiy, Mar 27 2020
Sum_{k=1..n} a(k) ~ c * n^2, where c = (Pi^2/12) * Product_{p prime} (1 + 1/p^2 - 2/p^3) = A072691 * A330594 = 0.910438... . - Amiram Eldar, Nov 01 2022
EXAMPLE
a(12) = (2+3)*(2+4) = 30.
MAPLE
A107759 := proc(n) local pf, p ; if n = 1 then 1; else pf := ifactors(n)[2] ; mul( 2+op(1, p)^op(2, p), p=pf) ; end if; end proc:
seq(A107759(n), n=1..60) ; # R. J. Mathar, Jan 07 2011
MATHEMATICA
a[1] = 1; a[n_] := Times @@ (2 + Power @@@ FactorInteger[n]); Array[a, 100] (* Amiram Eldar, Sep 20 2020 *)
CROSSREFS
KEYWORD
nonn,mult,easy
AUTHOR
Yasutoshi Kohmoto, May 25 2005
STATUS
approved