a(n) = Sum_{k=1..n} phi(k) * (floor(n/k)^4 - floor((n-1)/k)^4).

Terms

a(0) =1a(1) =16a(2) =67a(3) =192a(4) =373a(5) =768a(6) =1111a(7) =1904a(8) =2601a(9) =3872a(10) =4651a(11) =7280a(12) =7837a(13) =11056a(14) =13215a(15) =17024a(16) =18001a(17) =25488a(18) =25363a(19) =34624a(20) =37093a(21) =44576a(22) =45607a(23) =63440a(24) =60345a(25) =74368a(26) =79803a(27) =96432a(28) =92653a(29) =125616