A083288 Sigma unitary-sigma perfect numbers: numbers m which satisfy the following equation for some integer k: sigma(usigma(m)) = k*m where usigma(m) is sum of unitary divisors of m.
1, 2, 9, 15, 18, 21, 40, 42, 60, 104, 120, 288, 312, 756, 1023, 1170, 2160, 2520, 3024, 4092, 6048, 6552, 8184, 17850, 18720, 29127, 30690, 40768, 58254, 79794, 147312, 285600, 491040, 507780, 556920, 932064, 1276704, 1966020, 3300570, 4134780, 4194288, 4470648
Offset: 1
Keywords
Examples
9 is in the sequence since usigma(9) = 10 and sigma(10) = 18 = 2 * 9 is divisible by 9.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..71
Programs
-
Mathematica
usigma[1]=1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); Select[ Range[10^4], Divisible[DivisorSigma[1, usigma[#]], #] & ] (* Amiram Eldar, Jul 02 2019 *)
Extensions
More terms from Amiram Eldar, Jul 02 2019