a(n) is the number of hierarchical models on n unlabeled factors or variables with linear terms forced.

A006602

a(n) is the number of hierarchical models on n unlabeled factors or variables with linear terms forced.

Terms

    a(0) =2a(1) =1a(2) =2a(3) =5a(4) =20a(5) =180a(6) =16143a(7) =489996795

External references