Triangle relating to ordered Bell numbers, A000670.

Terms

a(0) =1a(1) =1a(2) =2a(3) =1a(4) =3a(5) =9a(6) =1a(7) =4a(8) =18a(9) =52a(10) =1a(11) =5a(12) =30a(13) =130a(14) =375a(15) =1a(16) =6a(17) =45a(18) =260a(19) =1125a(20) =3246a(21) =1a(22) =7a(23) =63a(24) =455a(25) =2625a(26) =11361a(27) =32781a(28) =1a(29) =8