A024963 a(n) = Sum(a(2i-1)*a(n-2i+1), i = 1,2,...,[ (n+2)/4 ]).

3, 1, 2, 6, 18, 58, 186, 594, 1898, 6390, 21402, 71350, 237522, 824130, 2840594, 9735090, 33326370, 117518870, 412260450, 1439364870, 5017074450, 17912831754, 63634522842, 225032003602, 794803982874, 2859133321638, 10244767026810, 36572931177942