a(n) = Sum_{k=0..n} binomial(n+k,k)*sin(Pi*(n+k)/2).

Terms

a(0) =0a(1) =1a(2) =-3a(3) =9a(4) =-30a(5) =106a(6) =-385a(7) =1421a(8) =-5304a(9) =19966a(10) =-75658a(11) =288222a(12) =-1102790a(13) =4234868a(14) =-16312773a(15) =63003869a(16) =-243896960a(17) =946066678a(18) =-3676303578a(19) =14308370014a(20) =-55768166380a(21) =217640082188a(22) =-850345208538