E.g.f. 1/((1-x)(1-x^4)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =48a(5) =240a(6) =1440a(7) =10080a(8) =120960a(9) =1088640a(10) =10886400a(11) =119750400a(12) =1916006400a(13) =24908083200a(14) =348713164800