a(n) = Product_{k = 1..n-1} (9*k - 4).

A147629

a(n) = Product_{k = 1..n-1} (9*k - 4).

Terms

    a(0) =1a(1) =5a(2) =70a(3) =1610a(4) =51520a(5) =2112320a(6) =105616000a(7) =6231344000a(8) =423731392000

External references