A124246 Numbers k that divide 5^k - 2.

1, 3, 123, 202884639, 242405133, 92273577267, 2670733723929, 81035221987959

Offset: 1

Author

Farideh Firoozbakht, Nov 19 2006

Keywords

• nonn

Comments

No other terms below 10^15. Some larger terms: 60092749466423900486673922957841, 401021769827858799355246286337987697472836927856337282726789534497163. - Max Alekseyev, Oct 15 2016

Crossrefs

Solutions to 5^n == k (mod n): A067946 (k=1), A015951 (k=-1), this sequence (k=2), A123062 (k=-2), A123061 (k=3), A123052 (k=-3), A125949 (k=4), A123047 (k=-4), A123091 (k=5), A015891 (k=-5), A277350 (k=6), A277348 (k=-6).

Programs

Mathematica

Do[If[Mod[(PowerMod[5,n,n]-2),n]==0,Print[n]],{n,1000000000}]

PARI

is(n)=Mod(5,n)^n==2 \\ Charles R Greathouse IV, Nov 04 2016

Extensions

a(6)-a(8) from Max Alekseyev, Jul 28 2009, Jun 02 2010, Oct 15 2016