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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =7a(5) =24a(6) =63a(7) =130a(8) =242a(9) =408a(10) =650a(11) =980a(12) =1425a(13) =2000a(14) =2737a(15) =3654a(16) =4788a(17) =6160a(18) =7812a(19) =9768a(20) =12075a(21) =14760a(22) =17875a(23) =21450a(24) =25542a(25) =30184a(26) =35438a(27) =41340a(28) =47957a(29) =55328