a(n) = Sum_{1 <= x_1 <= x_2 <= x_3 <= x_4 <= x_5 <= n} gcd(x_1, x_2, x_3 , x_4, x_5, n).

Terms

a(0) =1a(1) =7a(2) =23a(3) =64a(4) =130a(5) =287a(6) =468a(7) =864a(8) =1335a(9) =2156a(10) =3013a(11) =4790a(12) =6200a(13) =9072a(14) =11972a(15) =16440a(16) =20365a(17) =28209a(18) =33667a(19) =45014a(20) =54192a(21) =68853a(22) =80752a(23) =104964a(24) =119279a(25) =148778a(26) =172629a(27) =211252a(28) =237364a(29) =295288