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 A110509 #17 Aug 29 2017 22:50:36
%S A110509 1,0,1,0,-2,1,0,0,-4,1,0,0,4,-6,1,0,0,0,12,-8,1,0,0,0,-8,24,-10,1,0,0,
%T A110509 0,0,-32,40,-12,1,0,0,0,0,16,-80,60,-14,1,0,0,0,0,0,80,-160,84,-16,1,
%U A110509 0,0,0,0,0,-32,240,-280,112,-18,1,0,0,0,0,0,0,-192,560,-448,144,-20,1,0,0,0,0,0,0,64,-672,1120,-672,180,-22,1
%N A110509 Riordan array (1, x(1-2x)).
%C A110509 Inverse is Riordan array (1,xc(2x)) [A110510]. Row sums are A107920(n+1). Diagonal sums are (-1)^n*A052947(n).
%H A110509 G. C. Greubel, <a href="/A110509/b110509.txt">Table of n, a(n) for the first 50 rows, flattened</a>
%F A110509 Number triangle: T(n, k) = (-2)^(n-k)*binomial(k, n-k).
%F A110509 T(n,k) = A109466(n,k)*2^(n-k). - _Philippe Deléham_, Oct 26 2008
%e A110509 Rows begin
%e A110509 1;
%e A110509 0, 1;
%e A110509 0, -2, 1;
%e A110509 0, 0, -4, 1;
%e A110509 0, 0, 4, -6, 1;
%e A110509 0, 0, 0, 12, -8, 1;
%e A110509 0, 0, 0, -8, 24, -10, 1;
%t A110509 T[n_, k_] := (-2)^(n - k)*Binomial[k, n - k]; Table[T[n, k], {n, 0, 49}, {k, 0, n}] // Flatten (* _G. C. Greubel_, Aug 29 2017 *)
%o A110509 (PARI) for(n=0,25, for(k=0,n, print1((-2)^(n-k)*binomial(k, n-k), ", "))) \\ _G. C. Greubel_, Aug 29 2017
%K A110509 easy,sign,tabl
%O A110509 0,5
%A A110509 _Paul Barry_, Jul 24 2005