Number of vertices in a Farey fan of order n.

Terms

a(0) =4a(1) =6a(2) =11a(3) =17a(4) =29a(5) =39a(6) =59a(7) =79a(8) =107a(9) =133a(10) =175a(11) =213a(12) =271a(13) =323a(14) =385a(15) =451a(16) =541a(17) =621a(18) =731a(19) =835a(20) =955a(21) =1073a(22) =1225a(23) =1367a(24) =1541a(25) =1707a(26) =1897a(27) =2087a(28) =2321a(29) =2535