Bishops on a 2n+1 X 2n+1 board (see Robinson paper for details).

Terms

a(0) =1a(1) =2a(2) =6a(3) =18a(4) =60a(5) =200a(6) =760a(7) =2888a(8) =11856a(9) =48672a(10) =215904a(11) =957728a(12) =4506304a(13) =21203072a(14) =105494400a(15) =524880000a(16) =2737670400a(17) =14279148032a(18) =77836363264a(19) =424289980928