a(n) = Sum_{1 <= j <= n/2, gcd(j,n)=1} j^3.

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =9a(5) =1a(6) =36a(7) =28a(8) =73a(9) =28a(10) =225a(11) =126a(12) =441a(13) =153a(14) =416a(15) =496a(16) =1296a(17) =469a(18) =2025a(19) =1100a(20) =1710a(21) =1225a(22) =4356a(23) =1800a(24) =4959a(25) =2556a(26) =5581a(27) =4410a(28) =11025a(29) =3872