a(n) = 5*a(n-2), starting 1,2,4.

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =20a(5) =50a(6) =100a(7) =250a(8) =500a(9) =1250a(10) =2500a(11) =6250a(12) =12500a(13) =31250a(14) =62500a(15) =156250a(16) =312500a(17) =781250a(18) =1562500a(19) =3906250a(20) =7812500a(21) =19531250a(22) =39062500a(23) =97656250a(24) =195312500a(25) =488281250a(26) =976562500a(27) =2441406250a(28) =4882812500a(29) =12207031250