A184966 Numbers k such that k^k - 1 is squarefree.

2, 3, 4, 6, 7, 11, 12, 14, 15, 16, 20, 22, 23, 27, 31, 34, 35, 36, 38, 39, 42, 43, 47, 52, 56, 58, 59, 60, 63, 66, 67, 70, 71, 72, 75, 78, 79, 83, 84, 86, 87, 88, 90, 92, 94, 95, 96, 102, 103, 104, 106, 107, 108, 110, 111, 112, 114, 115, 119, 123, 128, 131, 135, 138

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Mar 19 2011

Keywords

• nonn

Comments

3^3 - 1 = 26 = 2 * 13.

4^4 - 1 = 255 = 3 * 5 * 17.

6^6 - 1 = 46655 = 5 * 7 * 31 * 43.

Crossrefs

Cf. A005117, A048861, A184967.

Programs

Mathematica

Select[Range@43, SquareFreeQ[#^# - 1] &]

PARI

isok(k) = issquarefree(k^k-1); \\ Michel Marcus, Feb 22 2021

Extensions

a(23)-a(64) from Amiram Eldar, Feb 22 2021