OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..100
EXAMPLE
Prime factors of 8580 are 2, 3, 5, 11, 13 and sigma(8580) = 28224, sigma(8580/2) + sigma(8580/3) + sigma(8580/5) + sigma(8580/11) + sigma(8580/13) = 12096 + 7056 + 4704 + 2352 + 2016 = 28224.
MAPLE
with(numtheory): P:=proc(q) local k, n; for n from 1 to q do
if sigma(n)=add(sigma(n/k), k=factorset(n)) then print(n);
fi; od; end: P(10^9);
MATHEMATICA
Select[Range[2, 60000], DivisorSigma[1, #] == Total@DivisorSigma[1, #/FactorInteger[#][[;; , 1]]] &] (* Amiram Eldar, Mar 20 2019 *)
PROG
(PARI) isok(x) = my(f=factor(x)[, 1]~); sigma(x) == sum(k=1, #f, sigma(x/f[k])); \\ Michel Marcus, Mar 15 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Mar 13 2019
STATUS
approved