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 A013721 #21 Sep 08 2022 08:44:38 %S A013721 16,4096,1048576,268435456,68719476736,17592186044416, %T A013721 4503599627370496,1152921504606846976,295147905179352825856, %U A013721 75557863725914323419136,19342813113834066795298816,4951760157141521099596496896 %N A013721 a(n) = 16^(2*n + 1). %H A013721 Vincenzo Librandi, <a href="/A013721/b013721.txt">Table of n, a(n) for n = 0..100</a> %H A013721 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a> %H A013721 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (256). %F A013721 From _Philippe Deléham_, Nov 27 2008: (Start) %F A013721 a(n) = 256*a(n-1); a(0)=16. %F A013721 G.f.: 16/(1-256*x). %F A013721 a(n) = 4*A013780(n). (End) %t A013721 NestList[256#&,16,20] (* _Harvey P. Dale_, Oct 28 2015 *) %o A013721 (Magma) [16^(2*n+1): n in [0..15]]; // _Vincenzo Librandi_, Jun 04 2011 %o A013721 (PARI) a(n)=16^(2*n+1) \\ _Charles R Greathouse IV_, Jul 11 2016 %K A013721 nonn,easy %O A013721 0,1 %A A013721 _N. J. A. Sloane_