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

Terms

a(0) =1a(1) =14a(2) =64a(3) =160a(4) =368a(5) =592a(6) =1104a(7) =1520a(8) =2400a(9) =3056a(10) =4640a(11) =5264a(12) =7824a(13) =8736a(14) =11776a(15) =13216a(16) =17984a(17) =18384a(18) =25344a(19) =26080a(20) =33312a(21) =35120a(22) =45584a(23) =44320a(24) =58480a(25) =58512a(26) =72000a(27) =73200a(28) =92624a(29) =86848