A055720 Numbers k such that d(k)+1 | k.

3, 4, 10, 15, 28, 35, 54, 55, 63, 64, 65, 85, 95, 98, 100, 115, 125, 135, 144, 145, 147, 155, 156, 175, 176, 185, 189, 205, 215, 234, 235, 245, 260, 265, 295, 297, 305, 335, 336, 351, 355, 364, 365, 395, 400, 408, 415, 416, 445, 459, 485

Offset: 1

Author

Robert G. Wilson v, Jun 09 2000

Keywords

• nonn

Comments

Integers divisible by 1 more than the number of their divisors. The only prime is 3.

These numbers cannot be very orderly numbers (A167409). - T. D. Noe, Nov 13 2009

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000005, A167409.

Programs

Mathematica

Select[Range[1000], Mod[ #, 1 + DivisorSigma[0, # ]] == 0 &]

PARI

isok(k) = Mod(k, numdiv(k)+1) == 0; \\ Michel Marcus, Mar 12 2020

Extensions

Edited by T. D. Noe, Nov 13 2009