The number of regions in a Farey diagram of order (n,n).

Terms

a(0) =4a(1) =56a(2) =504a(3) =2024a(4) =8064a(5) =18200a(6) =50736a(7) =99248a(8) =202688a(9) =343256a(10) =657904a(11) =983008a(12) =1708672a(13) =2485968a(14) =3755184a(15) =5289944a(16) =8069736a(17) =10539792a(18) =15387320a(19) =19913840a(20) =26879400a(21) =34370432a(22) =46978336a(23) =57382856a(24) =75750736a(25) =93121536a(26) =118109776a(27) =142846912a(28) =183039992a(29) =213504768