Boustrophedon transform of (-1)^n.

Terms

a(0) =1a(1) =0a(2) =0a(3) =1a(4) =0a(5) =5a(6) =10a(7) =61a(8) =280a(9) =1665a(10) =10470a(11) =73621a(12) =561660a(13) =4650425a(14) =41441530a(15) =395757181a(16) =4031082640a(17) =43626778785a(18) =499925138190