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 A124749 #3 Mar 30 2012 18:59:18 %S A124749 1,0,1,0,0,1,0,0,0,1,0,0,0,-1,1,0,0,0,0,-1,1,0,0,0,0,0,-1,1,0,0,0,0,0, %T A124749 0,-2,1,0,0,0,0,0,0,1,-2,1,0,0,0,0,0,0,0,1,-2,1,0,0,0,0,0,0,0,0,1,-3,1 %N A124749 Expansion of (1+x*y+x^2*y^2)/(1-x^3*y^3+x^4*y^3). %C A124749 Row sums are A124750. Diagonal sums are A124751. Inverse is A124752. %F A124749 Number triangle T(n,k)=C(floor(k/3),n-k)*(-1)^(n-k) %F A124749 G.f. of column k is x^k*(1-x)^floor(k/3); - _Paul Barry_, Dec 14 2006 %e A124749 Triangle begins %e A124749 1, %e A124749 0, 1, %e A124749 0, 0, 1, %e A124749 0, 0, 0, 1, %e A124749 0, 0, 0, -1, 1, %e A124749 0, 0, 0, 0, -1, 1, %e A124749 0, 0, 0, 0, 0, -1, 1, %e A124749 0, 0, 0, 0, 0, 0, -2, 1, %e A124749 0, 0, 0, 0, 0, 0, 1, -2, 1, %e A124749 0, 0, 0, 0, 0, 0, 0, 1, -2, 1, %e A124749 0, 0, 0, 0, 0, 0, 0, 0, 1, -3, 1 %Y A124749 Cf. A124744. %K A124749 easy,sign,tabl %O A124749 0,35 %A A124749 _Paul Barry_, Nov 06 2006