A387159 Odd numbers k such that A173557(k) = A173557(sigma(k)), where A173557(n) is multiplicative with a(p^e) = p-1 and sigma is the sum of divisors function.

1, 63, 135, 351, 875, 891, 999, 1647, 1859, 1971, 4239, 5211, 7479, 8451, 10719, 11367, 12339, 14607, 16317, 16551, 17847, 18171, 19791, 20439, 22103, 23679, 26919, 27951, 29511, 31131, 31407, 31487, 32427, 32751, 33399, 35667, 37287, 39231, 43767, 44739, 47331, 50571, 52191, 53811, 54459, 57319, 57699, 63207, 66771

Offset

1,2

Comments

Odd numbers k for which A173557(k) == A387157(k).

Links

Antti Karttunen, Table of n, a(n) for n = 1..10000

Index entries for sequences where odd perfect numbers must occur, if they exist at all

Index entries for sequences related to sigma(n)

Mathematica

A387159Q[k_] := OddQ[k] && #[k] == #[DivisorSigma[1, k]] & [Times @@ (FactorInteger[#][[All, 1]] - 1) &];
Select[Range[100000], A387159Q] (* Paolo Xausa, Aug 20 2025 *)

Prog

(PARI)
A173557(n) = factorback(apply(p -> p-1, factor(n)[, 1]));
is_A387159(n) = (n%2 && (A173557(sigma(n))==A173557(n)));

Crossrefs

Odd terms of A387158.

Cf. A000203, A173557, A387157.

Cf. also A351443, A353679, A386425.

Sequence in context: A044631 A045136 A031895 * A044314 A044695 A211850

Adjacent sequences: A387156 A387157 A387158 * A387160 A387161 A387162

Keyword

nonn

Author

Antti Karttunen, Aug 19 2025

Status

approved