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A123047 Numbers k that divide 5^k + 4. 16
1, 3, 129, 60767, 76433163, 454034821, 26675718567, 164304369911289 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
k must be odd since any power of 5 plus 4 is odd. - Robert G. Wilson v, Nov 14 2006
a(9) > 10^15. - Max Alekseyev, Oct 17 2016
Large term (may not be the next one): 3014733401203184049549. - Max Alekseyev, Oct 18 2013
LINKS
MATHEMATICA
Do[ If[ PowerMod[5, 2n - 1, 2n - 1] + 5 == 2n, Print[2n - 1]], {n, 10^9}] (* Robert G. Wilson v *)
PROG
(PARI) is(n)=Mod(5, n)^n==-4 \\ Charles R Greathouse IV, Nov 04 2016
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), A125949 (k=4), this sequence (k=-4), A123091 (k=5), A015891 (k=-5), A277350 (k=6), A277348 (k=-6).
Sequence in context: A300543 A300970 A300927 * A097420 A037119 A113558
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Nov 04 2006
EXTENSIONS
a(4) and a(5) from Robert G. Wilson v, Nov 14 2006
a(7) from Ryan Propper, Mar 23 2007
a(8) from Max Alekseyev, Oct 17 2016
STATUS
approved

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Last modified July 20 20:25 EDT 2024. Contains 374459 sequences. (Running on oeis4.)