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 A111806 #6 Jan 04 2014 19:49:18 %S A111806 1,-3,1,7,-6,1,-15,23,-9,1,31,-72,48,-12,1,-63,201,-198,82,-15,1,127, %T A111806 -522,699,-420,125,-18,1,-255,1291,-2223,1795,-765,177,-21,1,511, %U A111806 -3084,6562,-6768,3840,-1260,238,-24,1,-1023,7181,-18324,23276,-16758,7266,-1932,308,-27,1,2047,-16398,49029,-74616,65870 %N A111806 Riordan array (1/(1+3x+2x^2),x/(1+3x+2x^2)). %C A111806 Signed version of A110441. Factors as (1/(1+x),x/(1+x))*((1-x)/(1+x),x(1-x)/(1+x)), or inverse binomial transform of A080246. Inverse of little Schroeder number array A110440. Row sums are A108520. Diagonal sums are (-1)^n*A001906(n+1). %F A111806 T(n,k)=-3*T(n-1,k)+T(n-1,k-1)-2*T(n-2,k), T(0,0)=1, T(n,k)=0 if k<0 or if k>n. - _Philippe Deléham_, Jan 04 2013 %e A111806 Triangle starts %e A111806 1; %e A111806 -3,1; %e A111806 7,-6,1; %e A111806 -15,23,-9,1; %e A111806 31,-72,48,-12,1; %K A111806 easy,sign,tabl %O A111806 0,2 %A A111806 _Paul Barry_, Aug 18 2005