OFFSET
1,2
COMMENTS
Conjecture: For k > 1, k^(m + 1) == -1 (mod m) has an infinite number of positive solutions.
MATHEMATICA
Select[Range[719*10^5], PowerMod[5, #+1, #]==#-1&] (* Harvey P. Dale, Jul 03 2020 *)
PROG
(Magma) [n + 1: n in [0..2000000] | Modexp(5, n + 2, n + 1) eq n];
(PARI) isok(m) = Mod(5, m)^(m+1) == -1; \\ Jinyuan Wang, Nov 16 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Nov 08 2019
STATUS
approved