Number of 4-cycles in the n-Pell graph.

Terms

a(0) =0a(1) =0a(2) =1a(3) =8a(4) =40a(5) =164a(6) =601a(7) =2048a(8) =6632a(9) =20680a(10) =62633a(11) =185352a(12) =538272a(13) =1538892a(14) =4341905a(15) =12112960a(16) =33464240a(17) =91666192a(18) =249215921a(19) =673049800a(20) =1806888568a(21) =4824913652a(22) =12821690281a(23) =33922774464a(24) =89391291480a(25) =234694621656a(26) =614106591769