a(n) = floor( Gamma(n+1/2) ).

Terms

a(0) =1a(1) =0a(2) =1a(3) =3a(4) =11a(5) =52a(6) =287a(7) =1871a(8) =14034a(9) =119292a(10) =1133278a(11) =11899423a(12) =136843365a(13) =1710542068a(14) =23092317922a(15) =334838609873