Number of 5-covers of an unlabeled n-set.

Terms

a(0) =1a(1) =5a(2) =28a(3) =156a(4) =863a(5) =4571a(6) =22952a(7) =108182a(8) =477136a(9) =1969270a(10) =7625579a(11) =27804973a(12) =95858868a(13) =313747418a(14) =978734539a(15) =2920530663a(16) =8363945469a(17) =23057872913a(18) =61357278239a(19) =157985305473a(20) =394486861086a(21) =957156158394