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 A280507 #13 Feb 15 2021 22:39:45
%S A280507 0,0,1,1,1,1,0,0,7,7,6,6,6,6,7,7,1,1,0,0,0,0,1,1,6,6,7,7,7,7,6,6,19,
%T A280507 19,18,18,18,18,19,19,20,20,21,21,21,21,20,20,18,18,19,19,19,19,18,18,
%U A280507 21,21,20,20,20,20,21,21,21,21,20,20,20,20,21,21,18,18,19,19,19,19,18,18,20,20,21,21,21,21,20,20,19,19,18,18,18,18,19,19,6,6
%N A280507 a(n) = n XOR A193231(n).
%H A280507 Antti Karttunen, <a href="/A280507/b280507.txt">Table of n, a(n) for n = 0..16383</a>
%H A280507 <a href="/index/Bi#binary">Index entries for sequences related to binary expansion of n</a>
%H A280507 <a href="/index/Ge#GF2X">Index entries for sequences operating on polynomials in ring GF(2)[X]</a>
%F A280507 a(n) = A003987(n,A193231(n)) = n XOR A193231(n).
%F A280507 Other identities. For all n >= 0:
%F A280507 a(A193231(n)) = a(n).
%o A280507 (PARI)
%o A280507 A193231(n) = { my(x='x); subst(lift(Mod(1, 2)*subst(Pol(binary(n), x), x, 1+x)), x, 2) }; \\ From A193231
%o A280507 A280507(n) = bitxor(n,A193231(n)); \\ _Antti Karttunen_, Feb 15 2021
%o A280507 (Scheme) (define (A280507 n) (A003987bi n (A193231 n))) ;; Where A003987bi implements A003987 (bitwise-XOR).
%Y A280507 Cf. A003987, A193231, A280501, A280502, A280508.
%Y A280507 Cf. A118666 (positions of zeros).
%K A280507 nonn,base,look
%O A280507 0,9
%A A280507 _Antti Karttunen_, Jan 09 2017