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A125949
Numbers k that divide 5^k - 4.
8
1, 4769, 8563651, 300414792131, 2353957351049, 15960089894129, 452045914836301, 657236915690111
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
Solutions to 5^n == k (mod n): A067946 (k=1), A015951 (k=-1), A124246 (k=2), A123062 (k=-2), A123061 (k=3), A123052 (k=-3), this sequence (k=4), A123047 (k=-4), A123091 (k=5), A015891 (k=-5), A277350 (k=6), A277348 (k=-6).
Sequence in context: A260293 A031567 A031747 * A237214 A204727 A203546
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