Number of pairs of parallel diagonals in a regular n-gon.

Terms

a(0) =0a(1) =0a(2) =0a(3) =3a(4) =7a(5) =16a(6) =27a(7) =45a(8) =66a(9) =96a(10) =130a(11) =175a(12) =225a(13) =288a(14) =357a(15) =441a(16) =532a(17) =640a(18) =756a(19) =891a(20) =1035a(21) =1200a(22) =1375a(23) =1573a(24) =1782a(25) =2016a(26) =2262a(27) =2535a(28) =2821a(29) =3136