Erroneous version of A005217.

Terms

a(0) =1a(1) =2a(2) =4a(3) =21a(4) =55a(5) =151a(6) =447a(7) =1389a(8) =4502a(9) =15046a(10) =51505a(11) =179463a(12) =634086a(13) =2265014a(14) =8163125a(15) =29637903a(16) =108282989a(17) =397761507a(18) =1468063369a(19) =5441174511a(20) =20242989728a(21) =75566702558a(22) =282959337159