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

Author

Michel Marcus, Jun 16 2025

Keywords

• nonn

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

Examples

			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
		

Links

• David A. Corneth, PARI program

Crossrefs

Cf. A000203, A141645 (a subsequence).

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

Cf. A383758.

Programs

PARI

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

Extensions

More terms from David A. Corneth, Jun 16 2025