A066541 Number of normal subgroups of the group GL(2,Z_n) of invertible 2 X 2 matrices mod n (sequence A000252).

1, 3, 5, 12, 6, 17, 8, 46, 14, 22, 8, 82, 12, 28, 38, 112, 10, 48, 12, 116, 48, 28, 8, 386, 18, 44, 27, 140, 12, 162, 16, 232, 48, 38, 64, 234, 18, 42, 76, 596, 16, 196, 16, 140, 108, 28, 8, 1022, 24, 66, 66, 232, 12, 93, 64, 680, 72, 44, 8, 1032, 24, 56, 204

Offset: 1

Author

Sharon Sela (sharonsela(AT)hotmail.com), Jan 07 2002

Keywords

• nonn

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..100

Crossrefs

Cf. A000252, A066514, A316498.

Programs

GAP

Concatenation([1], List([2..20], n->Size(NormalSubgroups(GL(2, Integers mod n))))); # Andrew Howroyd, Jul 04 2018

Extensions

Terms a(16) and beyond from Andrew Howroyd, Jul 04 2018