Number of pairs of intersecting diagonals in the interior and exterior of a regular n-gon.

Terms

a(0) =0a(1) =1a(2) =5a(3) =15a(4) =42a(5) =94a(6) =189a(7) =340a(8) =572a(9) =903a(10) =1365a(11) =1981a(12) =2790a(13) =3820a(14) =5117a(15) =6714a(16) =8664a(17) =11005a(18) =13797a(19) =17083a(20) =20930a(21) =25386a(22) =30525a(23) =36400a(24) =43092a(25) =50659a(26) =59189a(27) =68745a(28) =79422a(29) =91288