A389458 Numbers whose sum of non-unitary divisors (A048146) is congruent to 2 modulo 4.

4, 8, 16, 32, 45, 64, 90, 117, 125, 128, 153, 180, 234, 245, 250, 256, 261, 306, 325, 333, 360, 369, 405, 425, 468, 477, 490, 500, 512, 522, 549, 605, 612, 637, 650, 657, 666, 720, 725, 738, 801, 810, 833, 845, 850, 873, 909, 925, 936, 954, 980, 981, 1000, 1017, 1024, 1025, 1044, 1053, 1098, 1210, 1224, 1233, 1274

Offset

1,1

Links

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

Mathematica

A389458Q[k_] := Mod[DivisorSigma[1, k] - Times @@ (Power @@@ FactorInteger[k] + 1), 4] == 2;
Select[Range[1500], A389458Q] (* Paolo Xausa, Oct 13 2025 *)

Prog

(PARI)
A034448(n) = { my(f=factorint(n)); prod(k=1, #f~, 1+(f[k, 1]^f[k, 2])); };
A048146(n) = (sigma(n)-A034448(n));
is_A389458(k) = (2==(A048146(k)%4));

Crossrefs

Cf. A048146.

Cf. also A191217, A069562, A389197, A389199.

Disjoint union of A000079\{1,2} and A389459.

Sequence in context: A088259 A123857 A217313 * A101434 A391751 A293780

Adjacent sequences: A389455 A389456 A389457 * A389459 A389460 A389461

Keyword

nonn

Author

Antti Karttunen, Oct 06 2025

Status

approved