a(n) = Sum_{1 <= x_1, x_2, x_3, x_4 <= n} ( n/gcd(x_1, x_2, x_3, x_4, n) )^3.

Terms

a(0) =1a(1) =121a(2) =2161a(3) =15481a(4) =78001a(5) =261481a(6) =823201a(7) =1981561a(8) =4726081a(9) =9438121a(10) =19485841a(11) =33454441a(12) =62746321a(13) =99607321a(14) =168560161a(15) =253639801a(16) =410333761a(17) =571855801a(18) =893864881a(19) =1207533481a(20) =1778937361a(21) =2357786761a(22) =3404813281a(23) =4282153321a(24) =6093828001a(25) =7592304841a(26) =10335939121