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 A099669 #22 Jun 01 2025 18:26:39
%S A099669 2,24,246,2468,24690,246912,2469134,24691356,246913578,2469135800,
%T A099669 24691358022,246913580244,2469135802466,24691358024688,
%U A099669 246913580246910,2469135802469132,24691358024691354,246913580246913576,2469135802469135798,24691358024691358020,246913580246913580242
%N A099669 Partial sums of repdigits of A002276.
%H A099669 Matthew House, <a href="/A099669/b099669.txt">Table of n, a(n) for n = 1..1000</a>
%H A099669 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (12,-21,10).
%F A099669 a(n) = (2/81)*(10^(n+1) - 9*n - 10). - R. Piyo (nagoya314(AT)yahoo.com), Dec 10 2004
%F A099669 a(n) = 12*a(n-1) - 21*a(n-2) + 10*a(n-3). - _Matthew House_, Jun 30 2016
%F A099669 G.f.: 2*x/((1 - x)^2*(1 - 10*x)). - _Ilya Gutkovskiy_, Jun 30 2016
%F A099669 From _Elmo R. Oliveira_, Apr 02 2025: (Start)
%F A099669 E.g.f.: 2*exp(x)*(10*exp(9*x) - 9*x - 10)/81.
%F A099669 a(n) = 2*A014824(n). (End)
%e A099669 2 + 22 + 222 + 2222 = a(4) = 2468.
%p A099669 A099669:=n->(2/81)*(10^(n+1) - 9*n - 10): seq(A099669(n), n=1..30); # _Wesley Ivan Hurt_, Apr 18 2017
%t A099669 <<NumberTheory`NumberTheoryFunctions` Table[{k, Table[Apply[Plus, Table[k*(10^n-1)/9, {n, 1, m}]], {m, 1, 35}]}, {k, 1, 9}]
%t A099669 Table[2/9*Sum[10^i - 1, {i, n}], {n, 18}] (* _Robert G. Wilson v_, Nov 20 2004 *)
%t A099669 LinearRecurrence[{12,-21,10},{2,24,246},30] (* _Harvey P. Dale_, Jun 01 2025 *)
%Y A099669 Cf. A002275-A002283, A014824, A057932.
%K A099669 base,nonn,easy
%O A099669 1,1
%A A099669 _Labos Elemer_, Nov 17 2004