Number of complete quadrangles on an n X n grid (or geoplane).

Terms

a(0) =0a(1) =1a(2) =78a(3) =1278a(4) =9498a(5) =47331a(6) =175952a(7) =545764a(8) =1461672a(9) =3507553a(10) =7701638a(11) =15773526a(12) =30375194a(13) =55695587a(14) =97777392a(15) =165310348a(16) =270478344a(17) =430196181a(18) =666685134a(19) =1010083690a(20) =1498720098a(21) =2182544223