Total number of torsion-free congruence subgroups of PSL(2,Z) of genus n.

Terms

a(0) =254a(1) =459a(2) =672a(3) =1809a(4) =1665a(5) =3028a(6) =1780a(7) =6216a(8) =2671a(9) =6711a(10) =4483a(11) =8450a(12) =4978a(13) =12447a(14) =4581a(15) =16743a(16) =8607a(17) =17453a(18) =4819a(19) =24287a(20) =9396a(21) =27542a(22) =11206a(23) =22798a(24) =6903