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 A099886 #10 Jul 13 2015 23:52:46
%S A099886 1,3,7,9,21,63,107,189,273,819,1911,2457,5189,15567,28123,46701,65793,
%T A099886 197379,460551,592137,1381653,4144959,7039851,12434877,17829905,
%U A099886 53489715,124809335,160469145,340873541,1022620623,1840690907
%N A099886 XOR binomial transform of A099885.
%C A099886 Many terms of this sequence are equal to 3 times another term! Why? The XOR BINOMIAL transform of this sequence is A099885. A099885 is the central terms of the rows of the XOR difference triangle of the powers of 2 (A099884).
%F A099886 a(n) = SumXOR_{k=0..n} SumXOR_{i=0..k\2} (C(n, k)mod 2) * (C(k\2, i) mod 2) * 2^((k+1)\2+k\2-i), where the SumXOR is the analog of summation under XOR and x\y stands for floor(x/y) (see Pari program).
%o A099886 (PARI) {a(n)=my(B);B=0;for(k=0,n, for(i=0,k\2, B=bitxor(B, binomial(n,k)%2*binomial(k\2,i)%2*2^((k+1)\2+k\2-i) )));B}
%Y A099886 Cf. A099884, A001317, A099885.
%K A099886 nonn
%O A099886 0,2
%A A099886 _Paul D. Hanna_, Oct 28 2004