a(n) = Sum_{d|n} phi(d^4).

Terms

a(0) =1a(1) =9a(2) =55a(3) =137a(4) =501a(5) =495a(6) =2059a(7) =2185a(8) =4429a(9) =4509a(10) =13311a(11) =7535a(12) =26365a(13) =18531a(14) =27555a(15) =34953a(16) =78609a(17) =39861a(18) =123463a(19) =68637a(20) =113245a(21) =119799a(22) =267675a(23) =120175a(24) =313001a(25) =237285a(26) =358723a(27) =282083a(28) =682893a(29) =247995