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 A013725 #32 Jul 12 2025 16:09:38 %S A013725 20,8000,3200000,1280000000,512000000000,204800000000000, %T A013725 81920000000000000,32768000000000000000,13107200000000000000000, %U A013725 5242880000000000000000000,2097152000000000000000000000,838860800000000000000000000000,335544320000000000000000000000000 %N A013725 a(n) = 20^(2*n + 1). %H A013725 Vincenzo Librandi, <a href="/A013725/b013725.txt">Table of n, a(n) for n = 0..200</a> %H A013725 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>. %H A013725 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (400). %F A013725 From _Philippe Deléham_, Nov 28 2008: (Start) %F A013725 a(n) = 400*a(n-1); a(0)=20. %F A013725 G.f.: 20/(1-400*x). (End) %F A013725 From _Elmo R. Oliveira_, Jul 10 2025: (Start) %F A013725 E.g.f.: 20*exp(400*x). %F A013725 a(n) = A004171(n)*A013715(n) = A009964(A005408(n)). (End) %p A013725 seq(20^(2*n+1),n=0..10); # _Nathaniel Johnston_, Jun 25 2011 %t A013725 NestList[400*# &, 20, 15] (* _Paolo Xausa_, Jul 12 2025 *) %o A013725 (Magma) [20^(2*n+1): n in [0..15]]; // _Vincenzo Librandi_, Jun 26 2011 %o A013725 (PARI) a(n)=20^(2*n+1) \\ _Charles R Greathouse IV_, Jul 11 2016 %Y A013725 Bisection of A009964 (20^n). %Y A013725 Cf. A004171, A005408, A013708-A013724, A013726-A013729. %K A013725 nonn,easy %O A013725 0,1 %A A013725 _N. J. A. Sloane_