A385075 Numbers k for which sigma(k - x) + sigma(k + x) = 9*k has at least one nonnegative solution.

361881, 792960, 835072, 837312, 846720, 917280, 944608, 946176, 1509236, 1517264, 1630880, 1635600, 1636614, 1697560, 1834560, 1914092, 1926336, 1927692, 1941264, 2387120, 2450112, 2474316, 2494464, 2546656, 2573088, 2624832, 2685394, 2705680, 2840468, 2913120, 2941009

Offset

1,1

Comments

At least one of sigma(k - x) >= 4.5*(k - x) or sigma(k+x) >= 4.5*(k + x) is true. - David A. Corneth, Jun 16 2025

Links

Table of n, a(n) for n=1..31.

David A. Corneth, PARI program

Example

361881 is in the sequence via k = 361881 and x = 358839 so k-x = 3042, k+x = 720720 and sigma(k - x) + sigma(k + x) = 7137 + 3249792 = 3256929 = 9*361881 = 9*k. - David A. Corneth, Jun 16 2025

Prog

(PARI) isok(k) = forstep(x=k-1, 0, -1, if (sigma(k - x) + sigma(k + x) == 9*k, return(1)));

Crossrefs

Cf. A000203, A141645 (a subsequence).

Cf. A383268, A384838, A384839, A384840, A384841.

Cf. A383758.

Sequence in context: A034630 A251298 A235197 * A263213 A109160 A269127

Adjacent sequences: A385072 A385073 A385074 * A385076 A385077 A385078

Keyword

nonn

Author

Michel Marcus, Jun 16 2025

Extensions

More terms from David A. Corneth, Jun 16 2025

Status

approved