cp's OEIS Frontend

A129493 Composite numbers k such that 3^k mod k is a power of 3.

%I A129493 #14 Sep 08 2022 08:45:30
%S A129493 6,10,12,14,18,22,24,26,30,33,34,36,38,39,46,51,54,56,57,58,62,63,66,
%T A129493 69,72,74,78,82,86,87,90,91,92,93,94,99,104,106,108,111,112,116,117,
%U A129493 118,120,121,122,123,124,129,132,134,135,141,142,144,146,148,154,158,159
%N A129493 Composite numbers k such that 3^k mod k is a power of 3.
%C A129493 Complement to composite numbers: 9, 15, 21, 25, 27, 28, 35, 42, 44, 45, 48, 49, 50, 52, 55, 60, 65, 68, 70, 75, ....
%H A129493 Robert Israel, <a href="/A129493/b129493.txt">Table of n, a(n) for n = 1..10000</a>
%e A129493 14 is a member of the sequence since 3^14 mod 14 = 9.
%p A129493 filter:= proc(n) local k;
%p A129493   if isprime(n) then return false fi;
%p A129493   k:= 3 &^ n mod n;
%p A129493   k > 1 and k = 3^padic:-ordp(k,3)
%p A129493 end proc:
%p A129493 select(filter, [$4..1000]); # _Robert Israel_, Dec 03 2019
%t A129493 Select[Range@ 161, IntegerQ@ Log[3, PowerMod[3, #, # ]] &]
%o A129493 (Magma) [k:k in [2..160]| not IsPrime(k)  and  not IsZero(a)  and (PrimeDivisors(a) eq [3]) where a is 3^k mod k ]; // _Marius A. Burtea_, Dec 04 2019
%Y A129493 Cf. A036236, A122780, A129492, A129494, A129495, A129496, A129497.
%K A129493 easy,nonn
%O A129493 1,1
%A A129493 _Robert G. Wilson v_, Apr 17 2007