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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =15a(5) =1a(6) =1a(7) =165a(8) =165a(9) =1a(10) =1a(11) =3465a(12) =38115a(13) =3465a(14) =1a(15) =1a(16) =49665a(17) =11472615a(18) =11472615a(19) =49665a(20) =1a(21) =1a(22) =844305a(23) =2795493855a(24) =58705370955a(25) =2795493855a(26) =844305a(27) =1a(28) =1a(29) =13125105