A354712 Nonprime numbers k such that the number of divisors of k divides k-1.

1, 4, 16, 21, 25, 33, 49, 57, 64, 65, 69, 77, 81, 85, 93, 100, 105, 121, 125, 129, 133, 141, 145, 161, 169, 175, 177, 185, 201, 205, 209, 213, 217, 221, 237, 249, 253, 265, 273, 289, 297, 301, 305, 309, 321, 325, 329, 341, 345, 361, 365, 377, 381, 385, 393, 413, 417, 437, 445, 453, 465

Offset: 1

Author

Max Alekseyev, Jun 03 2022

Keywords

• nonn

Comments

Nonprime numbers k such that k == 1 (mod A000005(k)).

Crossrefs

Nonprime terms of A354711.

Cf. A000005, A033950, A272872, A354714, A354715, A354716.

Programs

Mathematica

Select[Range[500], ! PrimeQ[#] && Divisible[# - 1, DivisorSigma[0, #]] &] (* Amiram Eldar, Jun 03 2022 *)