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 A323476 #12 Jul 19 2022 08:03:37
%S A323476 37,52,58,76,82,91,115,121,130,145,177,183,192,207,230,257,275,281,
%T A323476 290,305,328,355,364,391,404,410,416,431,437,446,461,484,511,520,547,
%U A323476 560,566,572,578,605,618,624,630,640,646,654,678,684,693,708,731,758,767
%N A323476 Positions of 3's in A306211.
%H A323476 Rémy Sigrist, <a href="/A323476/b323476.txt">Table of n, a(n) for n = 1..25000</a>
%H A323476 Rémy Sigrist, <a href="/A323476/a323476.txt">C program for A323476</a>
%t A323476 seq[n_] := seq[n] = If[n==1, {1}, Join[seq[n-1], Length /@ Split[seq[n-1]]] ];
%t A323476 Position[seq[26], 3] // Flatten (* _Jean-François Alcover_, Jul 19 2022 *)
%o A323476 (C) See Links section.
%Y A323476 Cf. A306211, A306222, A306223.
%K A323476 nonn
%O A323476 1,1
%A A323476 _N. J. A. Sloane_, Jan 29 2019