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 A013723 #24 Sep 08 2022 08:44:38 %S A013723 18,5832,1889568,612220032,198359290368,64268410079232, %T A013723 20822964865671168,6746640616477458432,2185911559738696531968, %U A013723 708235345355337676357632,229468251895129407139872768 %N A013723 a(n) = 18^(2*n + 1). %H A013723 Vincenzo Librandi, <a href="/A013723/b013723.txt">Table of n, a(n) for n = 0..200</a> %H A013723 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a> %H A013723 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (324). %F A013723 From _Philippe Deléham_, Nov 28 2008: (Start) %F A013723 a(n) = 324*a(n-1); a(0)=18. %F A013723 G.f.: 18/(1-324*x). (End) %p A013723 seq(18^(2*n+1),n=0..10); # _Nathaniel Johnston_, Jun 25 2011 %t A013723 18^(2*Range[0,20]+1) (* or *) NestList[324#&,18,20] (* _Harvey P. Dale_, Sep 28 2021 *) %o A013723 (Magma) [18^(2*n+1): n in [0..15]]; // _Vincenzo Librandi_, Jun 26 2011 %o A013723 (PARI) a(n)=18^(2*n+1) \\ _Charles R Greathouse IV_, Jul 11 2016 %Y A013723 Bisection of A001027 (18^n). %Y A013723 Cf. A013708-A013722, A013724-A013729. %K A013723 nonn,easy %O A013723 0,1 %A A013723 _N. J. A. Sloane_