a(n) = Sum_{1 <= i, j, k, l <= n} gcd(i,j,k,l).

Terms

a(0) =1a(1) =17a(2) =84a(3) =276a(4) =649a(5) =1417a(6) =2528a(7) =4432a(8) =7033a(9) =10905a(10) =15556a(11) =22836a(12) =30673a(13) =41729a(14) =54944a(15) =71968a(16) =89969a(17) =115457a(18) =140820a(19) =175444a(20) =212537a(21) =257113a(22) =302720a(23) =366160a(24) =426505a(25) =500873a(26) =580676a(27) =677108a(28) =769761a(29) =895377