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 A013898 #24 Sep 08 2022 08:44:38 %S A013898 21,85766121,350277500542221,1430568690241985328321, %T A013898 5842587018385982521381124421,23861715484377209601555171628930521, %U A013898 97453656071460446110921078004886769746621,398010574215107679422058885600836061208944572721,1625515384162495488635310116741260158419511738394408821 %N A013898 a(n) = 21^(5*n + 1). %C A013898 a(n) mod 10 == 1 (the least significant decimal digit of each term is 1). %H A013898 Vincenzo Librandi, <a href="/A013898/b013898.txt">Table of n, a(n) for n = 0..50</a> %H A013898 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a> %H A013898 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (4084101). %F A013898 a(n) = 4084101*a(n-1), a(0)=21. - _Vincenzo Librandi_, May 27 2011 %t A013898 NestList[4084101#&,21,10] (* _Harvey P. Dale_, Apr 17 2013 *) %o A013898 (Magma) [21^(5*n+1): n in [0..10]]; // _Vincenzo Librandi_, May 27 2011 %Y A013898 Cf. A009965. %K A013898 nonn %O A013898 0,1 %A A013898 _N. J. A. Sloane_