a(n) = 4*6^n+1.

Terms

a(0) =5a(1) =25a(2) =145a(3) =865a(4) =5185a(5) =31105a(6) =186625a(7) =1119745a(8) =6718465a(9) =40310785a(10) =241864705a(11) =1451188225a(12) =8707129345a(13) =52242776065a(14) =313456656385