A four product triangle sequence based on :a=3;f(n,a)=f(n - 1, a) + a*f(n - 2, a).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =28a(5) =1a(6) =1a(7) =532a(8) =532a(9) =1a(10) =1a(11) =21280a(12) =404320a(13) =21280a(14) =1a(15) =1a(16) =516040a(17) =392190400a(18) =392190400a(19) =516040a(20) =1a(21) =1a(22) =15997240a(23) =294829133200a(25) =294829133200a(26) =15997240a(27) =1a(28) =1a(29) =427715680