OFFSET
1,3
COMMENTS
FORMULA
a(p) = p for odd primes p (A065091).
EXAMPLE
a(6) = 18 because there are 3 arithmetic divisors of 6 (1, 3 and 6): sigma(1)/tau(1) = 1/1 = 1; sigma(3)/tau(3) = 4/2 = 2; sigma(6)/tau(6) = 12/4 = 3. Product of this divisors is 18.
MATHEMATICA
a[n_] := Times @@ Select[Divisors[n], Divisible[DivisorSigma[1, #], DivisorSigma[0, #]] &]; Array[a, 100] (* Amiram Eldar, Oct 15 2020 *)
PROG
(Magma) [&*[d: d in Divisors(n) | IsIntegral(&+Divisors(d) / #Divisors(d))]: n in [1..100]]
(PARI) a(n) = my(d=divisors(n)); prod(k=1, #d, if (sigma(d[k]) % numdiv(d[k]), 1, d[k])); \\ Michel Marcus, Oct 15 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Oct 14 2020
STATUS
approved