Number of subgroups of the group GL(2,Z_n) of invertible 2 X 2 matrices mod n (sequence A000252).

Terms

a(0) =1a(1) =6a(2) =55a(3) =234a(4) =466a(5) =758a(6) =1704a(7) =24587a(8) =6656a(9) =6718a(10) =6428a(11) =114210a(12) =17158a(13) =26180a(14) =135869a(15) =701426a(16) =33277a(17) =126920a(18) =52320a(19) =1341656a(20) =469872a(21) =87924a(22) =48976a(23) =50257306a(24) =140918a(25) =291060a(26) =348528a(27) =3952920a(28) =175438a(29) =3685062