a(n) = 5^(floor(n/2))+5^(floor(n/2)-1)-5^(floor((n-1)/3)).

Terms

a(0) =5a(1) =5a(2) =25a(3) =25a(4) =145a(5) =125a(6) =725a(7) =725a(8) =3625a(9) =3625a(10) =18625a(11) =18125a(12) =93125a(13) =93125a(14) =465625a(15) =465625a(16) =2340625a(17) =2328125a(18) =11703125a(19) =11703125a(20) =58515625a(21) =58515625a(22) =292890625a(23) =292578125a(24) =1464453125a(25) =1464453125a(26) =7322265625a(27) =7322265625a(28) =36619140625a(29) =36611328125