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 A050727 #22 Mar 08 2024 16:02:58
%S A050727 0,1,2,3,4,8,11,13,14,15,26
%N A050727 Numbers k such that the decimal expansion of 6^k contains no pair of consecutive equal digits (probably finite).
%C A050727 No additional terms up to 25000. - _Harvey P. Dale_, Oct 17 2011
%C A050727 No additional terms up to 100000. - _Michel Marcus_, Oct 16 2019
%C A050727 No additional terms up to 10^7. - _Lucas A. Brown_, Mar 02 2024
%e A050727 6^26 = 170581728179578208256 where no consecutive digits are equal.
%t A050727 Select[Range[120],!MemberQ[Differences[IntegerDigits[6^#]],0]&] (* _Harvey P. Dale_, Oct 17 2011 *)
%o A050727 (PARI) isok(n) = {my(d = digits(6^n), c = d[1]); for (i=2, #d, if (d[i] == c, return (0)); c = d[i];); return (1);} \\ _Michel Marcus_, Oct 16 2019
%o A050727 (Python)
%o A050727 try: from gmpy2 import mpz; x = mpz(1)
%o A050727 except: x = 1
%o A050727 print(0)
%o A050727 k = 1
%o A050727 while True:
%o A050727 print('\b'*42 + str(k), end='')
%o A050727 x *= 6 # x == 6**k
%o A050727 y, flag = x, True
%o A050727 y, a = divmod(y, 10)
%o A050727 while y > 6:
%o A050727 b = a
%o A050727 y, a = divmod(y, 10)
%o A050727 if a == b:
%o A050727 flag = False
%o A050727 break
%o A050727 if flag: print()
%o A050727 k += 1
%o A050727 # _Lucas A. Brown_, Mar 02 2024
%Y A050727 Cf. A000400, A030702, A046264, A046272.
%K A050727 nonn,base,more
%O A050727 1,3
%A A050727 _Patrick De Geest_, Sep 15 1999