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 A099671 #15 Apr 03 2025 11:51:03
%S A099671 4,48,492,4936,49380,493824,4938268,49382712,493827156,4938271600,
%T A099671 49382716044,493827160488,4938271604932,49382716049376,
%U A099671 493827160493820,4938271604938264,49382716049382708,493827160493827152,4938271604938271596,49382716049382716040,493827160493827160484
%N A099671 Partial sums of repdigits of A002278.
%H A099671 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (12,-21,10).
%F A099671 a(n) = (4/81)*(10^(n+1) - 9*n - 10). - R. Piyo (nagoya314(AT)yahoo.com), Dec 10 2004
%F A099671 From _Chai Wah Wu_, Feb 28 2018: (Start)
%F A099671 a(n) = 12*a(n-1) - 21*a(n-2) + 10*a(n-3) for n > 3.
%F A099671 G.f.: 4*x/((1 - x)^2*(1 - 10*x)). (End)
%F A099671 From _Elmo R. Oliveira_, Apr 03 2025: (Start)
%F A099671 E.g.f.: 4*exp(x)*(10*exp(9*x) - 9*x - 10)/81.
%F A099671 a(n) = 4*A014824(n). (End)
%e A099671 4 + 44 + 444 + 4444 + 44444 = a(5) = 49380.
%t A099671 <<NumberTheory`NumberTheoryFunctions` Table[{k, Table[Apply[Plus, Table[k*(10^n-1)/9, {n, 1, m}]], {m, 1, 35}]}, {k, 1, 9}]
%t A099671 Table[4/9*Sum[10^i - 1, {i, n}], {n, 18}] (* _Robert G. Wilson v_, Nov 20 2004 *)
%Y A099671 Cf. A002275-A002283, A014824, A057932.
%K A099671 base,nonn,easy
%O A099671 1,1
%A A099671 _Labos Elemer_, Nov 17 2004
%E A099671 More terms from _Elmo R. Oliveira_, Apr 03 2025