A068382 - OEIS

%I #21 Apr 04 2020 20:01:05

%S 1,2,4,8,10,16,20,32,40,50,64,80,100,110,128,136,160,164,200,220,250,

%T 256,272,320,328,400,440,500,512,544,550,610,640,656,680,800,820,880,

%U 1000,1024,1088,1100,1210,1220,1250,1280,1312,1360,1544,1600,1640,1760

%N Numbers k such that k divides 9^k - 1.

%C For all m the sequence includes 2^m, 10^m, 2*10^m, 10*2^m.

%H Seiichi Manyama, <a href="/A068382/b068382.txt">Table of n, a(n) for n = 1..5000</a>

%t Join[{1}, Select[Range[10000], PowerMod[9, #, #] == 1 &]] (* _Robert Price_, Apr 04 2020 *)

%o (PARI) isok(n) = Mod(9, n)^n == Mod(1, n); \\ _Michel Marcus_, May 06 2016

%Y Cf. A014945, A014946, A014949, A014950.

%K easy,nonn

%O 1,2

%A _Benoit Cloitre_, Mar 05 2002