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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
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
1,2
LINKS
EXAMPLE
9 is in the sequence since usigma(9) = 10 and sigma(10) = 18 = 2 * 9 is divisible by 9.
MATHEMATICA
usigma[1]=1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); Select[ Range[10^4], Divisible[DivisorSigma[1, usigma[#]], #] & ] (* Amiram Eldar, Jul 02 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Yasutoshi Kohmoto, Jun 05 2003
EXTENSIONS
More terms from Amiram Eldar, Jul 02 2019
STATUS
approved