OFFSET
1,2
COMMENTS
No other terms below 10^15. - Max Alekseyev, Oct 17 2016
MATHEMATICA
a(1) = 1; Do[ If[ PowerMod[5, 2n - 1, 2n - 1] - 4 == 0, Print[2n - 1]], {n, 10^9}]
PROG
(PARI) is(n)=Mod(5, n)^n==4 \\ Charles R Greathouse IV, May 15 2013
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Feb 04 2007
EXTENSIONS
a(4)-a(8) from Max Alekseyev, Jun 09 2010, Oct 17 2016
STATUS
approved