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 A334915 #18 May 24 2020 14:58:56
%S A334915 0,8,9,14,15,16,17,30,31,32,33,62,63,64,65,66,67,72,73,74,75,84,85,86,
%T A334915 87,92,93,94,95,96,97,98,99,104,105,106,107,116,117,118,119,124,125,
%U A334915 126,127,128,129,130,131,148,149,150,151,168,169,170,171,188,189
%N A334915 Numbers whose XOR-triangles have central zeros.
%C A334915 Depending on the binary length of n, the center of the XOR-triangle for n consists of a single cell or a 2 X 2 X 2 triangle pointing upwards or downwards.
%H A334915 Rémy Sigrist, <a href="/A334915/b334915.txt">Table of n, a(n) for n = 1..10000</a>
%H A334915 Rémy Sigrist, <a href="/A334915/a334915.png">Triangle illustrating the initial terms</a> (central 0's are rendered in yellow)
%H A334915 <a href="/index/Bi#binary">Index entries for sequences related to binary expansion of n</a>
%H A334915 <a href="/index/X#XOR-triangles">Index entries for sequences related to XOR-triangles</a>
%e A334915 The XOR-triangles for a(8) = 30 and a(18) = 72 are as follows:
%e A334915 . 1 1 1 1 0 1 0 0 1 0 0 0
%e A334915 . ---------
%e A334915 . 0 \ 0 0 / 1 1 0 1 1 0 0
%e A334915 . \ / / \
%e A334915 . 0 \ 0 / 1 1 1 / 0 \ 1 0
%e A334915 . \ / -----
%e A334915 . 0 1 0 1 1 1
%e A334915 .
%e A334915 . 1 1 0 0
%e A334915 .
%e A334915 . 1 0
%e A334915 .
%e A334915 . 1
%o A334915 (PARI) is(n) = {
%o A334915 my (h=#binary(n)-1, l=0, m);
%o A334915 while (abs(h-l)>1, n=bitxor(m=n, n\2); h-=2; l++);
%o A334915 if (h>l, bittest(n,h)==0 && bittest(n,l)==0,
%o A334915 h<l, bittest(n,h)==0 && bittest(n,l)==0 && bittest(m,l)==0,
%o A334915 bittest(n,h)==0
%o A334915 )
%o A334915 }
%Y A334915 Cf. A334769.
%K A334915 nonn,base
%O A334915 1,2
%A A334915 _Rémy Sigrist_, May 16 2020