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

Terms

a(0) =1a(1) =65a(2) =757a(3) =4225a(4) =16001a(5) =49205a(6) =119365a(7) =271489a(8) =554797a(9) =1040065a(10) =1783541a(11) =3198325a(12) =4850977a(13) =7758725a(14) =12112757a(15) =17392769a(16) =24211265a(17) =36061805a(18) =47162485a(19) =67604225a(20) =90359305a(21) =115930165a(22) =148291397a(23) =205517173a(24) =250266001a(25) =315313505a(26) =404686153a(27) =504317125a(28) =595481825