Number of doubly symmetric characteristic solutions to the n-queens problem.

Terms

a(0) =1a(1) =0a(2) =0a(3) =1a(4) =1a(5) =0a(6) =0a(7) =0a(8) =0a(9) =0a(10) =0a(11) =4a(12) =4a(13) =0a(14) =0a(15) =32a(16) =64a(17) =0a(18) =0a(19) =240a(20) =352a(21) =0a(22) =0a(23) =1664a(24) =1632a(25) =0a(26) =0a(27) =16448a(28) =21888a(29) =0