Number of solutions to +-1 +- 2 +- 3 +- ... +- n == n-1 (mod n).

Terms

a(0) =2a(1) =4a(2) =2a(3) =0a(4) =6a(5) =20a(6) =18a(7) =0a(8) =56a(9) =204a(10) =186a(11) =0a(12) =630a(13) =2340a(14) =2182a(15) =0a(16) =7710a(17) =29120a(18) =27594a(19) =0a(20) =99858a(21) =381300a(22) =364722a(23) =0a(24) =1342176a(25) =5162220a(26) =4971008a(27) =0a(28) =18512790a(29) =71582716