OFFSET
1,6
COMMENTS
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..20000
EXAMPLE
For n = 12, divisors d of 12: 1, 2, 3, 4, 6, 12;
corresponding sigma(d): 1, 3, 4, 7, 12, 28;
sigma(d) divides n for 4 divisors d: 1, 2, 3, 6;
a(12) = 1 + 2 + 3 + 6 = 12.
MATHEMATICA
a[n_] := DivisorSum[n, # &, Divisible[n, DivisorSigma[1, #]] &]; Array[a, 100] (* Amiram Eldar, Jul 21 2019 *)
PROG
(Magma) [&+[d: d in Divisors(n) | IsIntegral(n / SumOfDivisors(d))]: n in [1..100]]
(PARI) a(n) = sumdiv(n, d, d*(!(n % sigma(d)))); \\ Michel Marcus, Jul 19 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Jul 19 2019
STATUS
approved