%N Number of n-element unlabeled N-free posets of height k (1 <= k <= n).
%D Khamis, Soheir M., Height counting of unlabeled interval and N-free posets. Discrete Math. 275 (2004), no. 1-3, 165-175.
%Y Row sums of A202181.
%Y From the definition, this sequence should be the same as A003430. I do not understand why they differ - possibly a different definition of "N-free"?
%A _N. J. A. Sloane_, Dec 13 2011