A024959 a(n) = Sum(a(2i-1)*a(n-2i+1), i = 1,2,...,[ (n+2)/4 ]).

2, 1, 2, 4, 8, 20, 48, 112, 264, 688, 1760, 4432, 11136, 30208, 80160, 209344, 547584, 1498752, 4052224, 10840064, 28972416, 80315136, 220124160, 597656576, 1623036928, 4522262528, 12503194624, 34330329088, 94172397568, 264205592576, 735690285056