a(n) = f(n,n+4) where f is given in A034261.

Terms

a(0) =0a(1) =1a(2) =15a(3) =125a(4) =814a(5) =4641a(6) =24388a(7) =121380a(8) =581400a(9) =2707386a(10) =12339569a(11) =55304535a(12) =244567050a(13) =1069784625a(14) =4637437560a(15) =19951650840a(16) =85290143760a(17) =362608278750