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

Terms

a(0) =1a(1) =9a(2) =31a(3) =77a(4) =141a(5) =279a(6) =379a(7) =637a(8) =877a(9) =1269a(10) =1431a(11) =2387a(12) =2341a(13) =3411a(14) =4371a(15) =5181a(16) =5169a(17) =7893a(18) =7183a(19) =10857a(20) =11749a(21) =12879a(22) =12651a(23) =19747a(24) =18041a(25) =21069a(26) =24043a(27) =29183a(28) =25173a(29) =39339