A triangular decomposition of the double factorial numbers A001147.

Terms

a(0) =1a(1) =0a(2) =1a(3) =0a(4) =2a(5) =1a(6) =0a(7) =4a(8) =10a(9) =1a(10) =0a(11) =8a(12) =60a(13) =36a(14) =1a(15) =0a(16) =16a(17) =296a(18) =516a(19) =116a(20) =1a(21) =0a(22) =32a(23) =1328a(24) =5168a(25) =3508a(26) =358a(27) =1a(28) =0a(29) =64