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 A353143 #13 Apr 27 2022 19:48:14 %S A353143 0,1,23,1233,101113,2231213,123020013,10033101013,222120223013, %T A353143 12213312233013,1002032203113013,22112101201213013, %U A353143 1213132233100013013,100022303120201013013,2201230001311023013013,121100320102103233013013,3330220302313011113013013 %N A353143 Decimal repunits written in base 4. %F A353143 a(n) = A007090(A002275(n)). %o A353143 (PARI) a(n) = fromdigits(digits((10^n-1)/9, 4)); %Y A353143 Cf. A002275, A291962, A353142, A353144, A353145, A353146, A353147, A353148. %Y A353143 Cf. A002450, A007090. %K A353143 nonn,base,easy %O A353143 0,3 %A A353143 _Seiichi Manyama_, Apr 26 2022