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 A050725 #21 Oct 16 2019 06:18:03
%S A050725 0,1,2,3,4,5,6,7,10,11,14,15,16,17,18,24,27,28,33,34,40,52,63
%N A050725 Decimal expansion of 4^n contains no pair of consecutive equal digits (probably finite).
%C A050725 No additional terms up to 1200. - _Harvey P. Dale_, Mar 30 2011
%C A050725 No additional terms up to 100000. - _Michel Marcus_, Oct 16 2019
%C A050725 Half of even terms of A050723. - _Joerg Arndt_, Oct 16 2019
%e A050725 4^63 = 85070591730234615865843651857942052864.
%t A050725 Select[Range[0,70],FreeQ[Differences[IntegerDigits[4^#]],0]&] (* _Harvey P. Dale_, Jul 25 2013 *)
%o A050725 (PARI) isok(n) = {my(d = digits(4^n), c = d[1]); for (i=2, #d, if (d[i] == c, return (0)); c = d[i];); return (1);} \\ _Michel Marcus_, Oct 16 2019
%Y A050725 Cf. A000302, A030701, A046262, A046270.
%K A050725 nonn,base,more
%O A050725 1,3
%A A050725 _Patrick De Geest_, Sep 15 1999