An upper bound for linearized chord diagrams.

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =18a(5) =72a(6) =321a(7) =1680a(8) =9852a(9) =64168a(10) =457659a(11) =3543785a(12) =29578097a(13) =264623046a(14) =2525897073a(15) =25622275565a(16) =275257714175