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 A331832 #8 Jan 29 2020 01:42:07 %S A331832 1,3,9,11,23,29,33,41,43,47,53,59,69,71,83,89,101,103,109,113,129,131, %T A331832 137,139,149,151,157,163,181,191,197,199,211,227,233,239,249,251,263, %U A331832 269,281,283,293,307,311,317,331,349,353,367,373,379,383,389,397,401 %N A331832 Numbers k such that all the divisors of k have an odd number of 1's in their negabinary representations. %H A331832 Amiram Eldar, <a href="/A331832/b331832.txt">Table of n, a(n) for n = 1..10000</a> %e A331832 9 is a term since all of its divisors, 1, 3 and 9, or 1, 111, and 11001 in negabinary representation, have an odd number of 1's. %t A331832 negaBinWt[n_] := negaBinWt[n] = If[n==0, 0, negaBinWt[Quotient[n-1, -2]] + Mod[n, 2]]; odNegaBinQ[n_] := OddQ[negaBinWt[n]]; seqQ[n_] := AllTrue[Divisors[n], odNegaBinQ]; Select[Range[401],seqQ] %Y A331832 Subsequence of A268273. %Y A331832 Cf. A027615, A039724, A093696. %K A331832 nonn,base %O A331832 1,2 %A A331832 _Amiram Eldar_, Jan 28 2020