a(n) = (2*n+1)^floor((n-1)/2).

Terms

a(0) =1a(1) =1a(2) =1a(3) =7a(4) =9a(5) =121a(6) =169a(7) =3375a(8) =4913a(9) =130321a(10) =194481a(11) =6436343a(12) =9765625a(13) =387420489a(14) =594823321a(15) =27512614111a(16) =42618442977