a(n) = Sum_{1 <= x_1, x_2, x_3, x_4 <= n} gcd(x_1, x_2, x_3, x_4, n)^4.

Terms

a(0) =1a(1) =31a(2) =161a(3) =736a(4) =1249a(5) =4991a(6) =4801a(7) =15616a(8) =19521a(9) =38719a(10) =29281a(11) =118496a(12) =57121a(13) =148831a(14) =201089a(15) =311296a(16) =167041a(17) =605151a(18) =260641a(19) =919264a(20) =772961a(21) =907711a(22) =559681a(23) =2514176a(24) =1170625a(25) =1770751a(26) =2106081a(27) =3533536a(28) =1414561a(29) =6233759