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 A043880 #19 Feb 16 2024 14:39:34
%S A043880 4,20,33,36,49,52,84,97,100,113,116,129,135,148,161,164,177,180,193,
%T A043880 199,212,225,228,241,244,340,353,356,369,372,385,391,404,417,420,433,
%U A043880 436,449,455,468,481,484,497,500,513,519,543,545,548,561,564,596,609,612
%N A043880 Numbers k such that 0 and 1 occur juxtaposed in the base-4 representation of k but not of k+1.
%t A043880 SequencePosition[Table[If[SequenceCount[IntegerDigits[n,4],{0,1}]>0 || SequenceCount[ IntegerDigits[ n,4],{1,0}]>0,1,0],{n,600}],{1,0}][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Sep 14 2016 *)
%o A043880 (Python)
%o A043880 from sympy.ntheory.factor_ import digits
%o A043880 def has01or10(k):
%o A043880 s = "".join(map(str, digits(k, 4)[1:])); return "01" in s or "10" in s
%o A043880 def ok(n): return has01or10(n) and not has01or10(n+1)
%o A043880 print(list(filter(ok, range(613)))) # _Michael S. Branicky_, Apr 20 2021
%Y A043880 Cf. A007090, A044446.
%K A043880 nonn,base
%O A043880 1,1
%A A043880 _Clark Kimberling_