OFFSET
1,2
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = n + 1 for n = primes (A000040).
EXAMPLE
For n=4; Product_{d|4} (sigma(d)/d) = (sigma(1)/1)*(sigma(2)/2)*(sigma(4)/4) = (1/1)*(3/2)*(7/4) = 21/8; a(4) = 21.
MATHEMATICA
Array[Numerator@ Product[DivisorSigma[1, d]/d, {d, Divisors@ #}] &, 51] (* Michael De Vlieger, Jan 19 2019 *)
PROG
(Magma) [Numerator(&*[&+[c: c in Divisors(d)] / d: d in Divisors(n)]): n in [1..100]]
(PARI) a(n) = my(d=divisors(n)); numerator(prod(k=1, #d, sigma(d[k])/d[k])); \\ Michel Marcus, Dec 23 2018, May 11 2020
CROSSREFS
KEYWORD
nonn,frac
AUTHOR
Jaroslav Krizek, Dec 23 2018
STATUS
approved