Main diagonal of array in A098691.

Terms

a(0) =1a(1) =2a(2) =10a(3) =78a(4) =777a(5) =9800a(6) =149796a(7) =2690420a(8) =55555500a(9) =1296871224a(10) =33773107758a(11) =970753545580