A388024 Numbers k such that (sigma(k) - k) AND 2*k = 2*k, where AND is bitwise-and, A004198.

120, 180, 240, 672, 840, 1344, 1872, 2100, 2184, 2352, 2376, 2688, 2700, 3300, 4680, 4896, 5040, 5376, 5640, 5700, 6552, 6660, 7440, 8520, 9360, 9480, 9744, 9792, 10260, 10500, 10752, 11280, 12360, 12480, 13464, 13728, 14688, 14850, 16416, 17556, 17808, 18564, 18600, 18960, 19530, 19620, 19656, 20040, 20064, 20496

Offset

1,1

Comments

These seem to be much more common than the terms of A388022 and of A388026. Why?

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).

Formula

{k | A001065(k) AND 2*k = 2*k}.

Mathematica

A388024Q[k_] := BitAnd[2*k, DivisorSigma[1, k] - k] == 2*k;
Select[Range[25000], A388024Q] (* Paolo Xausa, Sep 15 2025 *)

Prog

(PARI) is_A388024(n) = (bitand(sigma(n)-n, 2*n)==2*n);

Crossrefs

Cf. A000203, A001065, A004198.

Subsequence of A023197.

Subsequence: A005820.

Cf. also A324649, A388022, A388026.

Sequence in context: A204830 A388036 A279088 * A337479 A388019 A322377

Adjacent sequences: A388021 A388022 A388023 * A388025 A388026 A388027

Keyword

nonn

Author

Antti Karttunen, Sep 15 2025

Status

approved