a(4*n)=5^n, a(4*n+1)=2*5^n, a(4*n+2)=3*5^n, a(4*n+3)=4*5^n.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =10a(6) =15a(7) =20a(8) =25a(9) =50a(10) =75a(11) =100a(12) =125a(13) =250a(14) =375a(15) =500a(16) =625a(17) =1250a(18) =1875a(19) =2500a(20) =3125a(21) =6250a(22) =9375a(23) =12500a(24) =15625a(25) =31250a(26) =46875a(27) =62500a(28) =78125a(29) =156250