Index of (the image of) the modular group Gamma(n) in PSL_2(Z).

Terms

a(0) =1a(1) =6a(2) =12a(3) =24a(4) =60a(5) =72a(6) =168a(7) =192a(8) =324a(9) =360a(10) =660a(11) =576a(12) =1092a(13) =1008a(14) =1440a(15) =1536a(16) =2448a(17) =1944a(18) =3420a(19) =2880a(20) =4032a(21) =3960a(22) =6072a(23) =4608a(24) =7500a(25) =6552a(26) =8748a(27) =8064a(28) =12180a(29) =8640