a(n) = (2*n+1)^9.

Terms

a(0) =1a(1) =19683a(2) =1953125a(3) =40353607a(4) =387420489a(5) =2357947691a(6) =10604499373a(7) =38443359375a(8) =118587876497a(9) =322687697779a(10) =794280046581