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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..71

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

Cf. A000203, A045795, A034448.

Sequence in context: A217367 A076208 A057481 * A272044 A304803 A184531

Adjacent sequences:  A083285 A083286 A083287 * A083289 A083290 A083291

KEYWORD

nonn

AUTHOR

Yasutoshi Kohmoto, Jun 05 2003

EXTENSIONS

More terms from Amiram Eldar, Jul 02 2019

STATUS

approved

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Last modified June 19 16:40 EDT 2021. Contains 345144 sequences. (Running on oeis4.)