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 A098210 #12 Sep 08 2022 08:45:14
%S A098210 0,15,1155,111555,11115555,1111155555,111111555555,11111115555555,
%T A098210 1111111155555555,111111111555555555,11111111115555555555,
%U A098210 1111111111155555555555,111111111111555555555555
%N A098210 a(n) = -1 + A093137(n)^2.
%H A098210 Vincenzo Librandi, <a href="/A098210/b098210.txt">Table of n, a(n) for n = 0..100</a>
%F A098210 a(n) = (1/9)*(10^n-1)*(5+10^n). - _Vincenzo Librandi_, Jun 02 2013
%e A098210 Like other -1 + square of near-repdigits give special digit patterns: (33333334^2) - 1 = 11111115555555.
%t A098210 Table[(1/9) (10^n - 1) (5 + 10^n), {n, 0, 25}] (* _Vincenzo Librandi_, Jun 02 2013 *)
%o A098210 (Magma) [(1/9)*(10^n-1)*(5+10^n): n in [0..15]]; // _Vincenzo Librandi_, Jun 02 2013
%Y A098210 Cf. A093137.
%K A098210 nonn,easy
%O A098210 0,2
%A A098210 _Labos Elemer_, Oct 20 2004