Main diagonal of A058735.

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =20a(5) =55a(6) =162a(7) =477a(8) =1450a(9) =4446a(10) =13858a(11) =43589a(12) =138515a(13) =443487a(14) =1430261a(15) =4640312a(16) =15137893a(17) =49620637a(18) =163360133a(19) =539904503a(20) =1790699059a(21) =5958280016a(22) =19883532941a(23) =66532519727a(24) =223177199775a(25) =750340752081