A product triangle sequence based on recursion:a=5; f(n,a)=(2*a+1)*f(n-1,a)+f(n-2,a).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =11a(5) =1a(6) =1a(7) =120a(8) =120a(9) =1a(10) =1a(11) =1309a(12) =14280a(13) =1309a(14) =1a(15) =1a(16) =14279a(17) =1699201a(18) =1699201a(19) =14279a(20) =1a(21) =1a(22) =155760a(23) =202190640a(24) =2205562898a(25) =202190640a(26) =155760a(27) =1a(28) =1a(29) =1699081