a(n) = Sum_{-n<i<n, -n<j<n, gcd{i,j}=1} (n-|i|)*(n-|j|).

Terms

a(0) =0a(1) =12a(2) =56a(3) =172a(4) =400a(5) =836a(6) =1496a(7) =2564a(8) =4080a(9) =6212a(10) =8984a(11) =12788a(12) =17488a(13) =23644a(14) =31112a(15) =40148a(16) =50912a(17) =64172a(18) =79448a(19) =97868a(20) =118912a(21) =143108a(22) =170504a(23) =202500a(24) =238080a(25) =278700a(26) =323864a(27) =374508a(28) =430272a(29) =493380