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 A117375 #6 Mar 05 2013 15:58:16
%S A117375 1,3,1,12,4,1,51,17,5,1,222,74,23,6,1,978,326,104,30,7,1,4338,1446,
%T A117375 468,142,38,8,1,19323,6441,2103,657,189,47,9,1,86310,28770,9447,3006,
%U A117375 903,246,57,10,1,386250,128750,42440,13670,4223,1217,314,68,11,1,1730832
%N A117375 Riordan array (1/(1-3x*c(x)),xc(x)), c(x) the g.f. of A000108.
%C A117375 Triangle factors as (1,xc(x))*(1/(1-3x),x). First row is A007854. Second row is A049027(n)-0^n. Row sums are A049027(n+1). Diagonal sums are A117376.
%F A117375 Number triangle T(0,0)=1, T(n,k)=[k<=n]*sum{j=0..n, (j/(n-j))*C(2n-j,n-j)[k<=j]*3^(j-k)}
%e A117375 Triangle begins
%e A117375 1,
%e A117375 3, 1,
%e A117375 12, 4, 1,
%e A117375 51, 17, 5, 1,
%e A117375 222, 74, 23, 6, 1,
%e A117375 978, 326, 104, 30, 7, 1,
%e A117375 4338, 1446, 468, 142, 38, 8, 1
%e A117375 Production array begins
%e A117375 3, 1
%e A117375 3, 1, 1
%e A117375 3, 1, 1, 1
%e A117375 3, 1, 1, 1, 1
%e A117375 3, 1, 1, 1, 1, 1
%e A117375 3, 1, 1, 1, 1, 1, 1
%e A117375 3, 1, 1, 1, 1, 1, 1, 1
%e A117375 3, 1, 1, 1, 1, 1, 1, 1, 1
%e A117375 ... - _Philippe Deléham_, Mar 05 2013
%K A117375 easy,nonn,tabl
%O A117375 0,2
%A A117375 _Paul Barry_, Mar 10 2006