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

Terms

a(0) =1a(1) =1a(2) =1a(3) =-1a(4) =-4a(5) =-5a(6) =6a(7) =36a(8) =46a(9) =-101a(10) =-515a(11) =-506a(12) =2554a(13) =9991a(14) =3067a(15) =-79915a(16) =-227056a(17) =205681a(18) =2841708a(19) =5134140a(20) =-18296153a(21) =-107927240a(22) =-66578269a(23) =1174691649a(24) =4059143386a(25) =-4667894370a(26) =-69377504739a(27) =-126787267800a(28) =669710503012a(30) =475781902203