a(n) = 5*a(n-2) for n > 2; a(1) = 4, a(2) = 5.

Terms

a(0) =4a(1) =5a(2) =20a(3) =25a(4) =100a(5) =125a(6) =500a(7) =625a(8) =2500a(9) =3125a(10) =12500a(11) =15625a(12) =62500a(13) =78125a(14) =312500a(15) =390625a(16) =1562500a(17) =1953125a(18) =7812500a(19) =9765625a(20) =39062500a(21) =48828125a(22) =195312500a(23) =244140625a(24) =976562500a(25) =1220703125a(26) =4882812500a(27) =6103515625a(28) =24414062500