Number of 6-block ordered bicoverings of an unlabeled n-set.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =90a(5) =1716a(6) =11350a(7) =49860a(8) =173745a(9) =519345a(10) =1389078a(11) =3411060a(12) =7821950a(13) =16949910a(14) =35013240a(15) =69404416a(16) =132703770a(17) =245767890a(18) =442372300a(19) =776064960a(20) =1330117230a(21) =2231754820a(22) =3672227850a(23) =5934754020a(24) =9432962515a(25) =14763202395