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 A094623 #23 Feb 22 2024 09:02:50
%S A094623 0,1,11,21,121,221,1221,2221,12221,22221,122221,222221,1222221,
%T A094623 2222221,12222221,22222221,122222221,222222221,1222222221,2222222221,
%U A094623 12222222221,22222222221,122222222221,222222222221,1222222222221
%N A094623 Expansion of g.f. x*(1+10*x)/((1-x)*(1-10*x^2)).
%C A094623 Previous name was: Sequence whose n-th term digits sum to n.
%C A094623 n-th term digits are reversals of A094624(n).
%H A094623 Paolo Xausa, <a href="/A094623/b094623.txt">Table of n, a(n) for n = 0..1000</a>
%H A094623 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,10,-10).
%F A094623 G.f.: x*(1+10*x)/((1-x)*(1-10*x^2)).
%F A094623 a(n) = (10^(n/2)/2)*(11/9 + 2*sqrt(10)/9 - (2*sqrt(10)/9 - 11/9)*(-1)^n) - 11/9.
%F A094623 E.g.f.: (11*(cosh(sqrt(10)*x) - cosh(x)) + 2*sqrt(10)*sinh(sqrt(10)*x) - 11*sinh(x))/9. - _Stefano Spezia_, Feb 21 2024
%t A094623 LinearRecurrence[{1, 10, -10}, {0, 1, 11}, 30] (* _Paolo Xausa_, Feb 22 2024 *)
%Y A094623 Cf. A094624, A094625, A094626.
%K A094623 easy,nonn,base
%O A094623 0,3
%A A094623 _Paul Barry_, May 15 2004