a(n) = Sum_{1 <= x_1, x_2, x_3 <= n} n/gcd(x_1, x_2, x_3, n).

Terms

a(0) =1a(1) =15a(2) =79a(3) =239a(4) =621a(5) =1185a(6) =2395a(7) =3823a(8) =6397a(9) =9315a(10) =14631a(11) =18881a(12) =28549a(13) =35925a(14) =49059a(15) =61167a(16) =83505a(17) =95955a(18) =130303a(19) =148419a(20) =189205a(21) =219465a(22) =279819a(23) =302017a(24) =388121a(25) =428235a(26) =518155a(27) =572405a(28) =707253a(29) =735885