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 A050724 #19 Mar 07 2024 16:39:53
%S A050724 0,1,2,3,4,5,6,7,8,9,10,13,14,15,16,17,18,21,22,24,26,42,66,67,133
%N A050724 Numbers k such that the decimal expansion of 3^k contains no pair of consecutive equal digits (probably finite).
%C A050724 No additional terms up to 50000. - _Harvey P. Dale_, Nov 15 2011
%C A050724 No additional terms up to 100000. - _Michel Marcus_, Oct 16 2019
%e A050724 3^133 = 2865014852390475710679572105323242035759805416923029389510561523.
%p A050724 q:= n-> (s-> andmap(i-> s[i]<>s[i+1], [$1..length(s)-1]))(""||(3^n)):
%p A050724 select(q, [$0..200])[]; # _Alois P. Heinz_, Mar 07 2024
%t A050724 Select[Range[0,500],!MemberQ[Differences[IntegerDigits[3^#]],0]&] (* _Harvey P. Dale_, Nov 15 2011 *)
%o A050724 (PARI) isok(n) = {my(d = digits(3^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 A050724 Cf. A000244, A030700, A046261, A046269.
%K A050724 nonn,base,more
%O A050724 1,3
%A A050724 _Patrick De Geest_, Sep 15 1999