A129497 - OEIS

%I #12 Jul 24 2021 05:39:06

%S 14,21,25,42,50,56,58,62,70,74,82,84,86,94,98,105,106,112,118,122,132,

%T 133,134,142,146,147,150,152,158,166,168,178,182,194,196,202,206,210,

%U 214,218,226,231,254,262,266,274,278,294,298,301,302,314,325,326,334

%N Composite numbers k such that 7^k (mod k) is a power of 7 greater than 1.

%H Amiram Eldar, <a href="/A129497/b129497.txt">Table of n, a(n) for n = 1..10000</a>

%e 58 is a member of the sequence since 7^58 (mod 58) == 49.

%t Select[Range@ 335, (p = PowerMod[7, #, #]) > 1 && IntegerQ@ Log[7, p] && CompositeQ[#] &] (* corrected by _Amiram Eldar_, Jul 24 2021 *)

%Y Cf. A036236, A129492, A129493, A129494, A129495, A129496.

%K easy,nonn

%O 1,1

%A _Robert G. Wilson v_, Apr 17 2007

%E Corrected and edited by _R. J. Mathar_, May 16 2008