Number of ways to express n in the form 1 +- 2 +- 3 ... +- n.

Terms

a(0) =1a(1) =0a(2) =0a(3) =1a(4) =2a(5) =0a(6) =0a(7) =6a(8) =11a(9) =0a(10) =0a(11) =57a(12) =103a(13) =0a(14) =0a(15) =615a(16) =1131a(17) =0a(18) =0a(19) =7209a(20) =13467a(21) =0a(22) =0a(23) =89261a(24) =168515a(25) =0a(26) =0a(27) =1147893a(28) =2183943a(29) =0