Number of parallelograms on an n X n grid.

Terms

a(0) =0a(1) =1a(2) =22a(3) =158a(4) =674a(5) =2159a(6) =5664a(7) =13004a(8) =26904a(9) =51401a(10) =92094a(11) =156710a(12) =255090a(13) =400359a(14) =608656a(15) =900100a(16) =1299336a(17) =1836461a(18) =2546550a(19) =3472162a(20) =4661898a(21) =6173123a(22) =8071952a(23) =10434600a(24) =13346080a(25) =16905033a(26) =21221558a(27) =26419338a(28) =32636098a(29) =40027283