Commuting elements: number of ordered pairs g, h in the group GL(2,Z_n) such that gh = hg.

Terms

a(0) =1a(1) =18a(2) =384a(3) =1344a(4) =11520a(5) =6912a(6) =96768a(7) =92160a(8) =303264a(9) =207360a(10) =1584000a(11) =516096a(12) =4402944a(13) =1741824a(14) =4423680a(15) =6094848a(16) =22560768a(17) =5458752a(18) =44323200a(19) =15482880a(20) =37158912a(21) =28512000a(22) =141064704a(23) =35389440a(24) =186000000a(25) =79252992a(26) =226748160a(27) =130056192a(28) =572947200a(29) =79626240