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 A323426 #22 Aug 31 2019 12:59:30 %S A323426 1,211,322111,4332221111,544333222211111,655444333322222111111, %T A323426 7665554444333332222221111111,877666555544444333333222222211111111 %N A323426 a(n) = decimal concatenation of n (once), n-1 (twice), n-2 (3 times), ..., 1 (n times). %C A323426 a(2), a(3) and a(4) are primes. %Y A323426 Cf. A098129. %K A323426 nonn,easy,base,less %O A323426 1,2 %A A323426 _Eder Vanzei_, Aug 30 2019