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 A331891 #12 Jan 31 2020 04:15:53 %S A331891 0,1,3,5,7,11,17,21,23,31,43,51,57,65,77,85,87,103,127,143,155,171, %T A331891 195,211,217,233,257,273,285,301,325,341,343,375,423,455,479,511,559, %U A331891 591,603,635,683,715,739,771,819,851,857,889,937,969,993,1025,1073,1105,1117 %N A331891 Negabinary palindromes: nonnegative numbers whose negabinary expansion (A039724) is palindromic. %C A331891 Numbers of the form 2^(2*m-1) - 1 (A083420) and 2^(2*m) + 1 (A052539) are terms. %H A331891 Amiram Eldar, <a href="/A331891/b331891.txt">Table of n, a(n) for n = 1..10000</a> %e A331891 5 is a term since its negabinary representation is 101 which is palindromic. %t A331891 negabin[n_] := negabin[n] = If[n==0, 0, negabin[Quotient[n-1, -2]]*10 + Mod[n, 2]]; Select[Range[0, 1200], PalindromeQ @ negabin[#] &] %Y A331891 Cf. A002113, A006995, A014190, A039724, A094202, A331191. %K A331891 nonn,base %O A331891 1,3 %A A331891 _Amiram Eldar_, Jan 30 2020