Number of 3-compositions of n.

Terms

a(0) =1a(1) =3a(2) =15a(3) =73a(4) =354a(5) =1716a(6) =8318a(7) =40320a(8) =195444a(9) =947380a(10) =4592256a(11) =22260144a(12) =107902088a(13) =523036176a(14) =2535324816a(15) =12289536016a(16) =59571339552a(17) =288761470848