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 A099673 #10 Apr 03 2025 02:55:24
%S A099673 6,72,738,7404,74070,740736,7407402,74074068,740740734,7407407400,
%T A099673 74074074066,740740740732,7407407407398,74074074074064,
%U A099673 740740740740730,7407407407407396,74074074074074062,740740740740740728,7407407407407407394,74074074074074074060,740740740740740740726
%N A099673 Partial sums of repdigits of A002280.
%H A099673 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (12,-21,10).
%F A099673 a(n) = (2/27)*(10^(n+1) - 9*n - 10). - R. Piyo (nagoya314(AT)yahoo.com), Dec 10 2004
%F A099673 From _Elmo R. Oliveira_, Apr 02 2025: (Start)
%F A099673 G.f.: 6*x/((1 - x)^2*(1 - 10*x)).
%F A099673 a(n) = 6*A014824(n).
%F A099673 E.g.f.: 2*exp(x)*(10*exp(9*x) - 9*x - 10)/27.
%F A099673 a(n) = 12*a(n-1) - 21*a(n-2) + 10*a(n-3) for n > 3. (End)
%e A099673 6 + 66 + 666 + 6666 + 66666 = a(5) = 74070.
%t A099673 <<NumberTheory`NumberTheoryFunctions` Table[{k, Table[Apply[Plus, Table[k*(10^n-1)/9, {n, 1, m}]], {m, 1, 35}]}, {k, 1, 9}]
%t A099673 Table[6/9*Sum[10^i - 1, {i, n}], {n, 18}] (* _Robert G. Wilson v_, Nov 20 2004 *)
%Y A099673 Cf. A002275-A002283, A014824, A057932, A099669-A099675.
%K A099673 base,nonn,easy
%O A099673 1,1
%A A099673 _Labos Elemer_, Nov 17 2004
%E A099673 More terms from _Elmo R. Oliveira_, Apr 02 2025