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 A331821 #8 Jan 28 2020 03:57:05
%S A331821 2,3,8,9,15,24,27,32,33,39,54,55,63,77,111,114,115,123,128,129,135,
%T A331821 144,159,174,175,203,234,235,245,255,264,294,295,329,370,371,384,413,
%U A331821 414,415,444,447,474,475,495,504,507,512,513,519,534,535,543,580,581,624
%N A331821 Positive numbers k such that -k and -(k + 1) are both negabinary-Niven numbers (A331728).
%H A331821 Amiram Eldar, <a href="/A331821/b331821.txt">Table of n, a(n) for n = 1..10000</a>
%e A331821 8 is a term since both -8 and -(8 + 1) = -9 are negabinary-Niven numbers: A039724(-8) = 1000 and 1 + 0 + 0 + 0 = 1 is a divisor of 8, and A039724(-9) = 1011 and 1 + 0 + 1 + 1 = 3 is a divisor of 9.
%t A331821 negaBinWt[n_] := negaBinWt[n] = If[n == 0, 0, negaBinWt[Quotient[n - 1, -2]] + Mod[n, 2]]; negaBinNivenQ[n_] := Divisible[n, negaBinWt[-n]]; c = 0; k = 1; s = {}; v = Table[-1, {2}]; While[c < 60, If[negaBinNivenQ[k], v = Join[Rest[v], {k}]; If[AllTrue[Differences[v], # == 1 &], c++; AppendTo[s, k - 1]]]; k++]; s
%Y A331821 Cf. A005352, A027615, A039724, A328209, A328213, A330927, A330931, A331086, A331089, A331728, A331819, A331820.
%K A331821 nonn,base
%O A331821 1,1
%A A331821 _Amiram Eldar_, Jan 27 2020