First difference of A002627.

Terms

a(0) =1a(1) =2a(2) =7a(3) =31a(4) =165a(5) =1031a(6) =7423a(7) =60621a(8) =554249a(9) =5611771a(10) =62353011a(11) =754471433a(12) =9876716941a(13) =139097096919