cp's OEIS Frontend

A125774 Numbers k such that 3^k mod k = 3^k mod k^2.

%I A125774 #17 Jun 19 2022 02:21:40
%S A125774 1,2,3,4,9,11,20,22,27,33,81,99,220,243,644,729,1220,2187,2420,5060,
%T A125774 6561,7128,8368,13420,14740,19683,23620,40573,55660,59049,145420,
%U A125774 147620,162140,177147,237820,259820,290620,308660,339020,447740,531441,548660
%N A125774 Numbers k such that 3^k mod k = 3^k mod k^2.
%C A125774 This sequence includes all powers of 3. a(2) = 2, a(3) = 3, a(6) = 11 and a(45) = 1006003 are the only known primes in this sequence.
%H A125774 Amiram Eldar, <a href="/A125774/b125774.txt">Table of n, a(n) for n = 1..400</a> (terms 1..100 from Harvey P. Dale)
%t A125774 Do[f=PowerMod[3,n,n];g=PowerMod[3,n,n^2];If[f==g,Print[n]],{n,1,1100000}]
%t A125774 Select[Range[600000],PowerMod[3,#,#]==PowerMod[3,#,#^2]&] (* _Harvey P. Dale_, Feb 21 2013 *)
%Y A125774 Cf. A014127 (Primes p such that p^2 divides 3^(p-1) - 1).
%Y A125774 Cf. A068535 (Numbers k such that 2^k mod k = 2^k mod k^2).
%Y A125774 Cf. A125773 (Numbers k, that are not powers of 2, such that 2^k mod k = 2^k mod k^2).
%Y A125774 Cf. A125775 (Numbers k such that 5^k mod k = 5^k mod k^2).
%K A125774 nonn
%O A125774 1,2
%A A125774 _Alexander Adamchuk_, Dec 07 2006