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 A061088 #9 Nov 09 2019 15:38:08
%S A061088 1,12,123,120304,102030405,10203040506,1020304050607,102030405060708,
%T A061088 10203040506070809,10203040506070809010,10203040506070809010011,
%U A061088 102030405060708009010011012,1020304050607008009010011012013,1020304050607008009010011012013014
%N A061088 a(n) = A053062(n) / n.
%H A061088 Andrew Howroyd, <a href="/A061088/b061088.txt">Table of n, a(n) for n = 1..100</a>
%e A061088 a(5) = 102030405 = 510152025/5, where 510152025 is obtained by concatenating 5,10,15,20 and finally 25 (which is 5^2).
%o A061088 (PARI) a(n)={fromdigits(concat(vector(n, k, digits(k*n))))/n} \\ _Andrew Howroyd_, Nov 09 2019
%Y A061088 Cf. A053062.
%K A061088 nonn,base
%O A061088 1,2
%A A061088 _Amarnath Murthy_, Apr 19 2001
%E A061088 Offset corrected and terms a(7) and beyond from _Andrew Howroyd_, Nov 09 2019