A388022 Numbers k such that sigma(k) AND 3*k = 3*k, where AND is bitwise-and, A004198.

120, 480, 672, 720, 960, 1344, 1800, 1920, 2352, 2688, 3840, 4680, 5220, 5376, 5616, 6840, 7344, 7680, 8880, 9600, 9720, 10296, 10752, 10944, 14256, 15360, 16416, 16560, 17100, 19200, 21504, 21888, 21960, 22032, 23280, 25440, 26160, 26496, 26820, 26880, 27360, 29568, 29880, 30720, 32472, 32832, 33120, 34560, 35760

Offset

1,1

Comments

When a term is present, then often many of its multiples are present also, for example, 1*120 = 120, 4*120 = 480, 6*120 = 720, 8*120 = 960, 15*120 = 1800, 16*120 = 1920, 32*120 = 3840, 39*120 = 4680, 57*120 = 6840 are all terms.

Links

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

Index entries for sequences related to binary expansion of n.

Index entries for sequences related to sigma(n).

Mathematica

A388022Q[k_] := BitAnd[3*k, DivisorSigma[1, k]] == 3*k;
Select[Range[40000], A388022Q] (* Paolo Xausa, Sep 15 2025 *)

Prog

(PARI) is_A388022(n) = (bitand(sigma(n), 3*n)==3*n);

Crossrefs

Cf. A000203, A004198.

Subsequence of A023197.

Subsequences: A005820, A388023 (terms of the form 4u+2), A388025 (primitive terms).

Cf. also A324652, A388017, A388024, A388026.

Sequence in context: A337469 A235232 A304284 * A167562 A033697 A157960

Adjacent sequences: A388019 A388020 A388021 * A388023 A388024 A388025

Keyword

nonn

Author

Antti Karttunen, Sep 15 2025

Status

approved