Number of solutions to +-1 +- 3 +- 5 +- 7 +- ... +- (4*n-1) = 0.

Terms

a(0) =1a(1) =0a(2) =2a(3) =2a(4) =8a(5) =20a(6) =68a(7) =206a(8) =692a(9) =2306a(10) =7930a(11) =27492a(12) =96792a(13) =343670a(14) =1231932a(15) =4447510a(16) =16164914a(17) =59086618a(18) =217091832a(19) =801247614a(20) =2969432270a(21) =11045446688a(22) =41224168020a(23) =154329373022a(24) =579377940390