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 A050730 #10 Sep 16 2024 17:13:57
%S A050730 0,1,2,3,4,5,7,8,9,11,12,13,21,33
%N A050730 Decimal expansion of 9^n contains no pair of consecutive equal digits (probably finite).
%e A050730 9^33 = 30903154382632612361920641803529.
%p A050730 q:= n-> (s-> andmap(i-> s[i]<>s[i+1], [$1..length(s)-1]))(""||(9^n)):
%p A050730 select(q, [$0..200])[]; # _Alois P. Heinz_, Mar 07 2024
%t A050730 Select[Range[0,350],FreeQ[Differences[IntegerDigits[9^#]],0]&] (* _Harvey P. Dale_, Sep 16 2024 *)
%Y A050730 Cf. A030705, A046267, A046275.
%K A050730 nonn,base
%O A050730 0,3
%A A050730 _Patrick De Geest_, Sep 15 1999