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 A095866 #9 May 16 2017 14:30:18
%S A095866 3,8,9,129,318,1008,2843,8988,38439,121089,42708,88208,2034819,
%T A095866 1749819,2235879,104271309,447194784,1234742858,2234186964,3266133123,
%U A095866 22172578524,114481278033,204796672749,841526085621,355055477499
%N A095866 Largest n-digit number - largest n-digit triangular number.
%H A095866 Harvey P. Dale, <a href="/A095866/b095866.txt">Table of n, a(n) for n = 1..1000</a>
%F A095866 a(n) = 10^n - 1 - A095864(n).
%t A095866 lndt[n_]:=Module[{c=Floor[(Sqrt[8*10^n+1]-1)/2]},(c(c+1))/2]; Join[{3}, Table[ 10^n-1-lndt[n],{n,2,30}]] (* _Harvey P. Dale_, May 16 2017 *)
%Y A095866 Cf. A068092, A068093, A068094, A095863, A095864, A095865.
%K A095866 base,easy,nonn
%O A095866 1,1
%A A095866 _Ray Chandler_, Jun 28 2004