Triangle T(n,k) giving number of (<=2)-covers of an n-set with k blocks.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =1a(5) =1a(6) =12a(7) =20a(8) =7a(9) =1a(10) =39a(11) =169a(12) =186a(13) =59a(14) =3a(15) =1a(16) =120a(17) =1160a(18) =2755a(19) =2243a(20) =661a(21) =55a(22) =1a(23) =363a(24) =7381a(25) =33270a(26) =52060a(27) =33604a(28) =9167a(29) =910