A387158 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, 6, 26, 28, 63, 74, 120, 122, 135, 146, 270, 314, 351, 386, 416, 496, 520, 554, 626, 672, 794, 842, 875, 891, 914, 999, 1080, 1082, 1226, 1232, 1322, 1346, 1404, 1466, 1480, 1514, 1638, 1647, 1750, 1754, 1782, 1859, 1971, 1994, 2186, 2306, 2402, 2426, 2440, 2474, 2642, 2762, 2906, 2920, 3242, 3314, 3506, 3718

Offset

1,2

Comments

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

A387158Q[k_] := #[k] == #[DivisorSigma[1, k]] & [Times @@ (FactorInteger[#][[All, 1]] - 1) &];
Select[Range[10000], A387158Q] (* Paolo Xausa, Aug 20 2025 *)

Prog

(PARI)
A173557(n) = factorback(apply(p -> p-1, factor(n)[, 1]));
is_A387158(n) = (A173557(sigma(n))==A173557(n));

Crossrefs

Cf. A000203, A173557, A387157.

Subsequences: A000396, A387159 (odd terms).

Cf. also A006872, A351446, A386424.

Sequence in context: A036175 A239178 A154869 * A043354 A023727 A045255

Adjacent sequences: A387155 A387156 A387157 * A387159 A387160 A387161

Keyword

nonn

Author

Antti Karttunen, Aug 19 2025

Status

approved