Whitney number of level n of the lattice of the ideals of the crown of size 2 n.

Terms

a(0) =2a(1) =1a(2) =1a(3) =4a(4) =9a(5) =21a(6) =52a(7) =127a(8) =313a(9) =778a(10) =1941a(11) =4863a(12) =12228a(13) =30837a(14) =77967a(15) =197574a(16) =501657a(17) =1275987a(18) =3250618a(19) =8292703a(20) =21182509a(21) =54169966a(22) =138674031a(23) =355343469a(24) =911347684a(25) =2339226871a(26) =6008781637a(27) =15445521202a(28) =39728258103a(29) =102248793573