Number of non-isomorphic set-systems of weight n with at least one singleton.

Terms

a(0) =0a(1) =1a(2) =1a(3) =3a(4) =6a(5) =14a(6) =32a(7) =79a(8) =193a(9) =499a(10) =1321a(11) =3626a(12) =10275a(13) =30126a(14) =91062a(15) =284093a(16) =912866a(17) =3018825a(18) =10261530a(19) =35814255a(20) =128197595a(21) =470146011a(22) =1764737593a(23) =6773539331a(24) =26561971320a(25) =106330997834a(26) =434195908353