a(n) = (n/4)*5^(n/2)*((1+sqrt(5))^2+(-1)^n*(1-sqrt(5))^2).

Terms

a(0) =0a(1) =5a(2) =30a(3) =75a(4) =300a(5) =625a(6) =2250a(7) =4375a(8) =15000a(9) =28125a(10) =93750a(11) =171875a(12) =562500a(13) =1015625a(14) =3281250a(15) =5859375a(16) =18750000a(17) =33203125a(18) =105468750a(19) =185546875a(20) =585937500a(21) =1025390625a(22) =3222656250a(23) =5615234375a(24) =17578125000a(25) =30517578125a(26) =95214843750a(27) =164794921875a(28) =512695312500a(29) =885009765625