login
A325471
a(n) is the product of divisors d of n such that d divides sigma(d).
4
1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 6, 1, 1, 1, 28, 1, 6, 1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 6, 1, 28, 1, 1, 1, 6, 1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 168, 1, 1
OFFSET
1,6
LINKS
FORMULA
a(A097603(n)) > 1.
EXAMPLE
For n = 12, divisors d of 12: 1, 2, 3, 4, 6, 12; corresponding sigma(d): 1, 3, 4, 7, 12, 28; d divides sigma(d) for 2 divisors d: 1 and 6; a(12) = 1 * 6 = 6.
MATHEMATICA
a[n_] := Times @@ Select[Divisors[n], Divisible[DivisorSigma[1, #], #] &]; Array[a, 100] (* Amiram Eldar, Aug 17 2019 *)
PROG
(Magma) [&*[d: d in Divisors(n) | IsIntegral(SumOfDivisors(d) / d)] : n in [1..100]]
(PARI) a(n)={vecprod([d | d<-divisors(n), sigma(d) % d==0])} \\ Andrew Howroyd, Aug 16 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Aug 16 2019
STATUS
approved