Main diagonal of A099239.

Terms

a(0) =1a(1) =2a(2) =8a(3) =41a(4) =250a(5) =1757a(6) =13917a(7) =122166a(8) =1173662a(9) =12222605a(10) =136927351a(11) =1639768418a(12) =20880556880a(13) =281460326864