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 A090173 #14 Oct 27 2021 15:02:47 %S A090173 0,0,1,0,1,1,0,0,1,0,0,1,1,1,1,0,1,1,1,1,1,0,0,0,1,1,0,0,0,1,0,0,1,0, %T A090173 0,1,0,1,1,1,1,1,1,1,1,0,0,1,1,1,1,1,1,1,0,0,1,1,1,1,1,1,1,1,1,1,0,1, %U A090173 1,0,1,1,1,1,1,0,1,1,0,0,0,0,0,1,1,1,1,0,0,0,0,0,1,0,0,0,1,1,1,1,1,0,0,0,1 %N A090173 Triangle read by rows, related to Pascal's triangle read mod 2, starting with 0, 0, 1. %H A090173 Y. Moshe, <a href="http://dx.doi.org/10.1016/S0022-314X(03)00103-3">The density of 0's in recurrence double sequences</a>, J. Number Theory, 103 (2003), 109-121; see Fig. 2. %F A090173 T(n, k) = T(n-1, k) + T(n-1, k-1) + T(n-2, k) + T(n-2, k-1) + T(n-2, k-2) for n >= 2, k >= 0, with initial conditions specified by first two rows. %e A090173 Triangle begins %e A090173 0; %e A090173 0,1; %e A090173 0,1,1; %e A090173 0,0,1,0; %e A090173 0,1,1,1,1; %e A090173 ... %Y A090173 Cf. A007318, A083093. %Y A090173 Cf. A090171, A090172, A090174, A091533, A091562, A205575 (same recurrence). %Y A090173 a(n, k) = A090174(n-1, k-1), k>0, 0 otherwise. %K A090173 nonn,easy,tabl %O A090173 0,1 %A A090173 _N. J. A. Sloane_, Jan 19 2004 %E A090173 Edited and extended by _Christian G. Bower_, Jan 20 2004