A392555 Numbers k such that k and k+2 are both 3-abundant numbers (A068403).

41509500030, 53751301758, 77545516048, 115021477998, 206704495998, 252375798400, 484648516350, 624285133470, 847528356400, 859086855198, 1040297484798, 1288792078000, 1386296806048, 1409258575998, 1631180701150, 1637022875488, 1682804950398, 1751559884800, 1850986110400, 1903522809760, 2041287696448

Offset

1,1

Comments

There are infinitely many odd terms in this sequence. Which odd term is the smallest?

Links

Table of n, a(n) for n=1..21.

Example

41509500030 is a term since sigma(41509500030) = 125179084800 > 124528500090 = 3 * 41509500030, and sigma(41509500032) = 126258048000 > 124528500096 = 3 * 41509500032.

Mathematica

isok[k_] := DivisorSigma[-1, k] > 3 && DivisorSigma[-1, k+2] > 3;

Prog

(PARI) isok(k) = sigma(k, -1) > 3 && sigma(k+2, -1) > 3;

Crossrefs

Subsequence of A068403 and A231086.

Cf. A000203 (sigma).

Sequence in context: A377456 A199428 A287261 * A172631 A172721 A259350

Adjacent sequences: A392552 A392553 A392554 * A392556 A392557 A392558

Keyword

nonn

Author

Amiram Eldar, Jan 16 2026

Status

approved