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5^p - 4^p - 1, where p is prime.
2

%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