A198915 - OEIS

%I #24 Jul 09 2023 11:20:59

%S 3,57,261633,18014398375264257,

%T 5846006549323611672814736913013492849365380759553

%N a(n) = 1 - 2^k + 4^k where k = 3^n.

%H Vincenzo Librandi, <a href="/A198915/b198915.txt">Table of n, a(n) for n = 0..6</a>

%H Dario A. Alpern, <a href="https://www.alpertron.com.ar/MODFERM.HTM">Factors of Generalized Fermat Numbers</a>

%p A198915:=n->4^(3^n) - 2^(3^n) + 1: seq(A198915(n), n=0..6); # _Wesley Ivan Hurt_, May 03 2017

%t Table[4^(3^n) - 2^(3^n) + 1, {n, 0, 5}]

%o (PARI) a(n)=1<<(2*3^n)-1<<3^n+1 \\ _Charles R Greathouse IV_, Oct 31 2011

%o (Magma) [4^(3^n) - 2^(3^n) + 1: n in [0..7]]; // _Vincenzo Librandi_, Jun 29 2014

%Y Cf. A051154.

%K nonn,easy

%O 0,1

%A _Artur Jasinski_, Oct 31 2011