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 A073791 #20 Jan 15 2024 11:04:36
%S A073791 0,1,2,3,-4,-3,-2,-1,-8,-7,-6,-5,-12,-11,-10,-9,16,17,18,19,12,13,14,
%T A073791 15,8,9,10,11,4,5,6,7,32,33,34,35,28,29,30,31,24,25,26,27,20,21,22,23,
%U A073791 48,49,50,51,44,45,46,47,40,41,42,43,36,37,38,39,-64,-63,-62,-61,-68,-67,-66,-65,-72,-71,-70,-69
%N A073791 Replace 4^k with (-4)^k in base 4 expansion of n.
%C A073791 Base 4 representation for n converted from base -4 to base 10.
%H A073791 Dana G. Korssjoen, Biyao Li, Stefan Steinerberger, Raghavendra Tripathi, and Ruimin Zhang, <a href="https://arxiv.org/abs/2012.04625">Finding structure in sequences of real numbers via graph theory: a problem list</a>, arXiv:2012.04625 [math.CO], 2020-2021.
%F A073791 a(4*k+m) = -4*a(k)+m for 0 <= m < 4. - _Chai Wah Wu_, Jan 16 2020
%t A073791 f[n_Integer, b_Integer] := Block[{l = IntegerDigits[n]}, Sum[l[[ -i]]*(-b)^(i - 1), {i, 1, Length[l]}]]; a = Table[ FromDigits[ IntegerDigits[n, 4]], {n, 0, 80}]; b = {}; Do[b = Append[b, f[a[[n]], 4]], {n, 1, 80}]; b
%o A073791 (PARI) a(n) = subst(Pol(digits(n,4)), x, -4); \\ _Michel Marcus_, Jan 30 2019
%Y A073791 Cf. A007090, A007608, A053985, A065369, A073792, A073793, A073794, A073795, A073796 & A073835.
%Y A073791 Cf. A066321, A320283.
%K A073791 base,easy,sign
%O A073791 0,3
%A A073791 _Robert G. Wilson v_, Aug 12 2002