a(n) = Sum_{1 <= x_1, x_2, x_3 <= n} ( n/gcd(x_1, x_2, x_3, n) )^2.

Terms

a(0) =1a(1) =29a(2) =235a(3) =925a(4) =3101a(5) =6815a(6) =16759a(7) =29597a(8) =57097a(9) =89929a(10) =160931a(11) =217375a(12) =371125a(13) =486011a(14) =728735a(15) =947101a(16) =1419569a(17) =1655813a(18) =2475739a(19) =2868425a(20) =3938365a(21) =4666999a(22) =6435815a(23) =6955295a(24) =9690601a(25) =10762625a(26) =13874563a(27) =15502075a(28) =20510309a(29) =21133315