Number of set partitions of set-systems with total sum n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =6a(5) =11a(6) =26a(7) =42a(8) =78a(9) =148a(10) =280a(11) =481a(12) =867a(13) =1569a(14) =2742a(15) =4933a(16) =8493a(17) =14857a(18) =25925a(19) =44877a(20) =77022a(21) =132511a(22) =226449a(23) =385396a(24) =657314a(25) =1111115a(26) =1875708a(27) =3157379a(28) =5309439a(29) =8885889