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

Terms

a(0) =1a(1) =2a(2) =4a(3) =12a(4) =36a(5) =120a(6) =400a(7) =1520a(8) =5776a(9) =23712a(10) =97344a(11) =431808a(12) =1915456a(13) =9012608a(14) =42406144a(15) =210988800a(16) =1049760000a(17) =5475340800a(18) =28558296064a(19) =155672726528a(20) =848579961856