Number of inequivalent ways (mod D_4) a pair of checkers can be placed on an n X n board.

Terms

a(0) =0a(1) =2a(2) =8a(3) =21a(4) =49a(5) =93a(6) =171a(7) =278a(8) =446a(9) =660a(10) =970a(11) =1347a(12) =1863a(13) =2471a(14) =3269a(15) =4188a(16) =5356a(17) =6678a(18) =8316a(19) =10145a(20) =12365a(21) =14817a(22) =17743a(23) =20946a(24) =24714a(25) =28808a(26) =33566a(27) =38703a(28) =44611a(29) =50955