Alternating sum of large Schroeder numbers.

Terms

a(0) =1a(1) =1a(2) =5a(3) =17a(4) =73a(5) =321a(6) =1485a(7) =7073a(8) =34513a(9) =171585a(10) =866133a(11) =4427313a(12) =22870425a(13) =119208321a(14) =626178717a(15) =3311424321a(16) =17615732385a(17) =94202293633a(18) =506116560293