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 A102572 #17 Sep 08 2022 08:45:16
%S A102572 0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
%T A102572 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,3,3,3,3,3,
%U A102572 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3
%N A102572 a(n) = floor(log_4(n)).
%F A102572 G.f.: (1/(1 - x))*Sum_{k>=1} x^(4^k). - _Ilya Gutkovskiy_, Jan 08 2017
%o A102572 (Magma) [ Ilog(4,n) : n in [1..150] ];
%o A102572 (PARI) a(n)=#digits(n,4)-1 \\ Twice as fast as a(n)=for(i=0,n,(n>>=2)||return(i)); the naïve code a(n)=log(n)\log(4) works for standard realprecision=28 only up to n=4^47-5 and it is slower by another factor 2. - _M. F. Hasler_, Mar 11 2015
%o A102572 (PARI) A102572(n)=logint(n,4) \\ _M. F. Hasler_, Nov 07 2019
%Y A102572 Cf. A000523, A062153.
%K A102572 nonn
%O A102572 1,16
%A A102572 _N. J. A. Sloane_, Dec 23 2006