|
%I #21 Jun 28 2021 04:06:05
%S 1,5,25,125,625,1555,3125,7775,15625,38875,78125,194375,390625,483605,
%T 971875,1953125,2418025,4859375,9673655,9765625,12090125,24296875,
%U 48368275,48828125,60450625,120909025,121484375,150401155,241841375
%N Numbers k that divide 6^k-1.
%C Includes all powers of 5. If a term such as 1555 = 5*311 occurs, so does any number of the form 5^a * 311^b for a>3.
%C From _Alexander Adamchuk_, May 16 2010: (Start)
%C All terms that are not powers of 5 are divisible by 5 and 311.
%C Prime divisors of a(n) are {5, 311, 6221, 15551, 155501, ...}. (End)
%t Select[ Range[ 5*10^7], PowerMod[6, #, # ] == 1 & ]
%o (PARI) is(n)=Mod(6,n)^n==1 \\ _Charles R Greathouse IV_, Nov 04 2016
%Y Cf. A024062 (6^n-1).
%K nonn
%O 1,2
%A _Olivier Gérard_
%E Better description from _Benoit Cloitre_, Mar 06 2002
%E Edited and extended by _Robert G. Wilson v_, Jun 18 2002
%E a(25)-a(45) from _Alexander Adamchuk_, May 16 2010
|
