OFFSET
1,2
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..407
EXAMPLE
Multiply-perfect number 672 is in sequence because 672 / tau(672) = 28 (integer).
MATHEMATICA
q[n_] := Module[{d = DivisorSigma[0, n], s = DivisorSigma[1, n]}, Divisible[s, n] && Divisible[n, d]]; Select[Range[31000], q] (* Amiram Eldar, May 09 2024 *)
PROG
(Magma) [n:n in [A007691(n)] | (Denominator((n/(#[d: d in Divisors(n)]))-(SumOfDivisors(n)/n))) eq 1]
(PARI) isok(n) = !(n % numdiv(n)) && !(sigma(n) % n); \\ Michel Marcus, Aug 11 2014
(PARI) is(k) = {my(f = factor(k), s = sigma(f), d = numdiv(f)); !(s % k) && !(k % d); } \\ Amiram Eldar, May 09 2024
CROSSREFS
Supersequence of A047728.
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Aug 01 2014
EXTENSIONS
a(14)-a(18) from Amiram Eldar, May 09 2024
STATUS
approved