a(n) = Sum_{k = 0..n} (-1)^k * binomial(n,k) * binomial(2*n,k).

Terms

a(0) =1a(1) =-1a(2) =-1a(3) =8a(4) =-17a(5) =-1a(6) =116a(7) =-344a(8) =239a(9) =1709a(10) =-7001a(11) =9316a(12) =22276a(13) =-138412a(14) =268568a(15) =189008a(16) =-2608913a(17) =6809417a(18) =-1814851a(19) =-45852416a(20) =159116983a(21) =-155628353a(22) =-720492928a(23) =3481793888a(24) =-5558713852a(25) =-9029921876a(26) =71541001076a(27) =-158672882224a(28) =-45300345128