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 A013780 #21 Sep 08 2022 08:44:38 %S A013780 4,1024,262144,67108864,17179869184,4398046511104,1125899906842624, %T A013780 288230376151711744,73786976294838206464,18889465931478580854784, %U A013780 4835703278458516698824704,1237940039285380274899124224 %N A013780 a(n) = 4^(4*n + 1). %H A013780 Vincenzo Librandi, <a href="/A013780/b013780.txt">Table of n, a(n) for n = 0..200</a> %H A013780 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a> %H A013780 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (256). %F A013780 From _Philippe Deléham_, Nov 27 2008: (Start) %F A013780 a(n) = 256*a(n-1); a(0)=4. %F A013780 G.f.: 4/(1-256*x). (End) %t A013780 NestList[256#&,4,20] (* _Harvey P. Dale_, Aug 09 2013 *) %o A013780 (Magma) [4^(4*n+1): n in [0..15]]; // _Vincenzo Librandi_, Jun 17 2011 %o A013780 (PARI) a(n)=4^(4*n+1) \\ _Charles R Greathouse IV_, Jul 11 2016 %K A013780 nonn,easy %O A013780 0,1 %A A013780 _N. J. A. Sloane_