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 A113999 #16 Jun 26 2024 04:25:42
%S A113999 1,11,101,1011,10001,100111,1000001,10001011,100000101,1000010011,
%T A113999 10000000001,100000101111,1000000000001,10000001000011,
%U A113999 100000000010101,1000000010001011,10000000000000001,100000000100100111
%N A113999 a(n) = Sum_{ k, k|n } 10^(k-1).
%C A113999 A034729 to base 2. Stacking elements of the sequence gives A113998.
%H A113999 Seiichi Manyama, <a href="/A113999/b113999.txt">Table of n, a(n) for n = 1..1000</a>
%F A113999 G.f.: Sum_{n>0} x^n/(1-10*x^n).
%F A113999 a(n) ~ 10^(n-1). - _Vaclav Kotesovec_, Jun 05 2021
%t A113999 A113999[n_]:= DivisorSum[n, 10^(#-1) &];
%t A113999 Table[A113999[n], {n, 40}] (* _G. C. Greubel_, Jun 26 2024 *)
%o A113999 (PARI) a(n)=if(n<1,0,sumdiv(n,k,10^(k-1)));
%o A113999 (Magma)
%o A113999 A113999:= func< n | (&+[10^(d-1): d in Divisors(n)]) >;
%o A113999 [A113999(n): n in [1..40]]; // _G. C. Greubel_, Jun 26 2024
%o A113999 (SageMath)
%o A113999 def A113999(n): return sum(10^(k-1) for k in (1..n) if (k).divides(n))
%o A113999 [A113999(n) for n in range(1,41)] # _G. C. Greubel_, Jun 26 2024
%Y A113999 Sums of the form Sum_{d|n} q^(d-1): A034729 (q=2), A034730 (q=3), this sequence (q=10), A339684 (q=4), A339685 (q=5), A339686 (q=6), A339687 (q=7), A339688 (q=8), A339689 (q=9).
%K A113999 easy,nonn
%O A113999 1,2
%A A113999 _Paul Barry_, Nov 12 2005