Sum of the denominators of the Farey series of order n (A006843).

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =18a(5) =38a(6) =50a(7) =92a(8) =124a(9) =178a(10) =218a(11) =328a(12) =376a(13) =532a(14) =616a(15) =736a(16) =864a(17) =1136a(18) =1244a(19) =1586a(20) =1746a(21) =1998a(22) =2218a(23) =2724a(24) =2916a(25) =3416a(26) =3728a(27) =4214a(28) =4550a(29) =5362