OFFSET
1,1
COMMENTS
3^3 - 1 = 26 = 2 * 13.
4^4 - 1 = 255 = 3 * 5 * 17.
6^6 - 1 = 46655 = 5 * 7 * 31 * 43.
MATHEMATICA
Select[Range@43, SquareFreeQ[#^# - 1] &]
PROG
(PARI) isok(k) = issquarefree(k^k-1); \\ Michel Marcus, Feb 22 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, Mar 19 2011
EXTENSIONS
a(23)-a(64) from Amiram Eldar, Feb 22 2021
STATUS
approved