Number of trapezoids on an n X n grid (or geoboard).

Terms

a(0) =0a(1) =1a(2) =50a(3) =490a(4) =2618a(5) =9519a(6) =28432a(7) =70796a(8) =157912a(9) =321161a(10) =610482a(11) =1082570a(12) =1848362a(13) =3003015a(14) =4716792a(15) =7204604a(16) =10730528a(17) =15530189a(18) =22093410a(19) =30723078a(20) =42146178a(21) =56981411a(22) =75952240a(23) =99685104a(24) =129757248