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Primes of the form 5^n - 4^n.
2

%I #23 May 14 2022 20:23:10

%S 61,1136791005963704961126617632861,

%T 173472015290681763212224222187425603741981,

%U 31861838222649045530727106406255616308752331078816472270207782250106896363274089867800367051529351065966102374800998198276889145001421

%N Primes of the form 5^n - 4^n.

%C All terms are odd, and if n is even, then 5^n - 4^n is divisible by 3. [_Vincenzo Librandi_, Nov 25 2010]

%C The next term (a(5)) has 156 digits. - _Harvey P. Dale_, May 14 2022

%H Muniru A Asiru, <a href="/A147667/b147667.txt">Table of n, a(n) for n = 1..9</a>

%e 5^3 - 4^3 = 125 - 64 = 61.

%p select(isprime, [seq(5^n - 4^n, n=0..200)]); # _Muniru A Asiru_, Mar 04 2018

%t lst={};Do[p=5^n-4^n;If[PrimeQ[p],AppendTo[lst,p]],{n,6!}];lst

%t Select[Table[5^n-4^n,{n,300}],PrimeQ] (* _Harvey P. Dale_, May 14 2022 *)

%o (GAP) Filtered(List([1..200],n->5^n - 4^n),IsPrime); # _Muniru A Asiru_, Mar 04 2018

%Y Cf. A059802 (corresponding n).

%K nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, Nov 10 2008