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 A073787 #11 Feb 16 2025 08:32:46
%S A073787 0,1,2,3,4,5,150,151,152,153,154,155,140,141,142,143,144,145,130,131,
%T A073787 132,133,134,135,120,121,122,123,124,125,110,111,112,113,114,115,100,
%U A073787 101,102,103,104,105,250,251,252,253,254,255,240,241,242,243,244,245
%N A073787 Numbers in base -6.
%D A073787 D. E. Knuth, The Art of Computer Programming. Addison-Wesley, Reading, MA, 1969, Vol. 2, p. 189.
%H A073787 Chai Wah Wu, <a href="/A073787/b073787.txt">Table of n, a(n) for n = 0..10000</a>
%H A073787 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Negabinary.html">Negabinary</a>
%H A073787 Prepared and presented by Matthew Szudzik of Wolfram Research, <a href="http://library.wolfram.com/conferences/devconf99/challenge/">A Mathematica programming contest</a>
%t A073787 ToNegaBases[i_Integer, b_Integer] := FromDigits[ Rest[ Reverse[ Mod[ NestWhileList[(#1 - Mod[ #1, b])/-b &, i, #1 != 0 &], b]]]]; Table[ ToNegaBases[n, 6], {n, 0, 60}]
%o A073787 (Python)
%o A073787 def A073787(n):
%o A073787 s, q = '', n
%o A073787 while q >= 6 or q < 0:
%o A073787 q, r = divmod(q, -6)
%o A073787 if r < 0:
%o A073787 q += 1
%o A073787 r += 6
%o A073787 s += str(r)
%o A073787 return int(str(q)+s[::-1]) # _Chai Wah Wu_, Apr 09 2016
%Y A073787 Cf. A007092, A039724, A073785, A007608, A073786, A073788, A073789, A073790 & A039723.
%K A073787 base,easy,nonn
%O A073787 0,3
%A A073787 _Robert G. Wilson v_, Aug 11 2002