Main diagonal of A090806.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =9a(5) =20a(6) =45a(7) =100a(8) =220a(9) =478a(10) =1025a(11) =2169a(12) =4534a(13) =9364a(14) =19125a(15) =38646a(16) =77306a(17) =153173a(18) =300765a(19) =585518a(20) =1130612a(21) =2166284a(22) =4120062a(23) =7780817a(24) =14595364a(25) =27201794a(26) =50383690a(27) =92768457a(28) =169835952a(29) =309223286