This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A198915 #24 Jul 09 2023 11:20:59
%S A198915 3,57,261633,18014398375264257,
%T A198915 5846006549323611672814736913013492849365380759553
%N A198915 a(n) = 1 - 2^k + 4^k where k = 3^n.
%H A198915 Vincenzo Librandi, <a href="/A198915/b198915.txt">Table of n, a(n) for n = 0..6</a>
%H A198915 Dario A. Alpern, <a href="https://www.alpertron.com.ar/MODFERM.HTM">Factors of Generalized Fermat Numbers</a>
%p A198915 A198915:=n->4^(3^n) - 2^(3^n) + 1: seq(A198915(n), n=0..6); # _Wesley Ivan Hurt_, May 03 2017
%t A198915 Table[4^(3^n) - 2^(3^n) + 1, {n, 0, 5}]
%o A198915 (PARI) a(n)=1<<(2*3^n)-1<<3^n+1 \\ _Charles R Greathouse IV_, Oct 31 2011
%o A198915 (Magma) [4^(3^n) - 2^(3^n) + 1: n in [0..7]]; // _Vincenzo Librandi_, Jun 29 2014
%Y A198915 Cf. A051154.
%K A198915 nonn,easy
%O A198915 0,1
%A A198915 _Artur Jasinski_, Oct 31 2011