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 A014905 #33 Mar 31 2025 15:37:46
%S A014905 1,23,486,10210,214415,4502721,94557148,1985700116,41699702445,
%T A014905 875693751355,18389568778466,386180944347798,8109799831303771,
%U A014905 170305796457379205,3576421725604963320,75104856237704229736,1577201980991788824473,33121241600827565313951,695546073617378871592990
%N A014905 a(1)=1, a(n) = 21*a(n-1) + n.
%H A014905 Vincenzo Librandi, <a href="/A014905/b014905.txt">Table of n, a(n) for n = 1..200</a>
%H A014905 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (23,-43,21).
%F A014905 a(1)=1, a(2)=23, a(3)=486, a(n) = 23*a(n-1) - 43*a(n-2) + 21*a(n-3). - _Vincenzo Librandi_, Oct 19 2012
%F A014905 From _Elmo R. Oliveira_, Mar 29 2025: (Start)
%F A014905 G.f.: x/((1-21*x)*(x-1)^2).
%F A014905 E.g.f.: exp(x)*(21*exp(20*x) - 20*x - 21)/400.
%F A014905 a(n) = (21^(n+1) - 20*n - 21)/400. (End)
%t A014905 LinearRecurrence[{23, -43, 21}, {1, 23, 486}, 20] (* _Vincenzo Librandi_, Oct 19 2012 *)
%o A014905 (Magma) I:=[1, 23, 486]; [n le 3 select I[n] else 23*Self(n-1) - 43*Self(n-2)+ 21*Self(n-3): n in [1..20]]; // _Vincenzo Librandi_, Oct 19 2012
%Y A014905 Row n=21 of A126885.
%K A014905 nonn,easy
%O A014905 1,2
%A A014905 _N. J. A. Sloane_, _Olivier Gérard_