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 A328749 #17 Apr 13 2023 02:35:37
%S A328749 0,-1,1,-2,-3,-1,2,1,3,-4,-5,-3,-6,-7,-5,-2,-3,-1,4,3,5,2,1,3,6,5,7,
%T A328749 -8,-9,-7,-10,-11,-9,-6,-7,-5,-12,-13,-11,-14,-15,-13,-10,-11,-9,-4,
%U A328749 -5,-3,-6,-7,-5,-2,-3,-1,8,7,9,6,5,7,10,9,11,4,3,5,2,1,3,6
%N A328749 a(n) = Sum_{k = 0..w and t_k > 0} (-1)^t_k * 2^k, where Sum_{k = 0..w} t_k * 3^k is the ternary representation of n.
%C A328749 Every integer appears in the sequence.
%H A328749 Rémy Sigrist, <a href="/A328749/b328749.txt">Table of n, a(n) for n = 0..6561</a>
%F A328749 a(n) = 0 iff n = 0.
%F A328749 a(n) > 0 iff n belongs to A157671.
%F A328749 a(n) < 0 iff n belongs to A132141.
%F A328749 a(A004488(n)) = -a(n).
%e A328749 a(42) = a(1*3^3 + 1*3^2 + 2*3^1) = -2^3 - 2^2 + 2^1 = -10.
%o A328749 (PARI) a(n) = my (d=Vecrev(digits(n,3))); sum(i=1, #d, if (d[i], (2^i) * (-1)^d[i], 0))/2
%o A328749 (Python)
%o A328749 from sympy.ntheory.factor_ import digits
%o A328749 def A328749(n): return sum((-(1<<i) if j&1 else 1<<i) for i, j in enumerate(digits(n,3)[-1:0:-1]) if j>0) # _Chai Wah Wu_, Apr 12 2023
%Y A328749 Cf. A004488, A132141, A157671, A328728.
%K A328749 sign,base
%O A328749 0,4
%A A328749 _Rémy Sigrist_, Oct 27 2019