%I #13 Sep 08 2022 08:46:08
%S 8,60,2100,61740,44633820,1153594260,745759583940,18798608421180,
%T 11850560210900460,185976284546943991380,4652001187058965190220,
%U 72740686675902780452348340,45469899385367953379053128420
%N 5^p - 4^p - 1, where p is prime.
%C For p>3 all terms are divisible by 21.
%H Vincenzo Librandi, <a href="/A242084/b242084.txt">Table of n, a(n) for n = 1..100</a>
%F a(n) = A054401(A000040(n)). - _Michel Marcus_, May 05 2014
%t Table[5^Prime[n] - 4^Prime[n] - 1, {n, 1, 60}]
%o (Magma) [5^p-4^p-1: p in PrimesUpTo(60)];
%o (PARI) a(n) = my(p = prime(n)); 5^p - 4^p - 1; \\ _Michel Marcus_, May 05 2014
%Y Cf. A204768.
%K nonn,less
%O 1,1
%A _Vincenzo Librandi_, May 04 2014