Duplicate of A071969.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =19a(5) =63a(6) =219a(7) =787a(8) =2897a(9) =10869a(10) =41414a(11) =159822a(12) =623391a(13) =2453727a(14) =9733866a(15) =38877318a(16) =156206233a(17) =630947421a(18) =2560537092a(19) =10435207116a(20) =42689715279a(21) =175243923783a(22) =721649457417