A202181 Triangle read by rows: T(n,k) = number of n-element unlabeled N-free posets of height k (1 <= k <= n).

1, 1, 1, 1, 3, 1, 1, 7, 6, 1, 1, 13, 24, 10, 1, 1, 25, 77, 61, 15, 1, 1, 43, 228, 291, 130, 21, 1, 1, 76, 644, 1229, 856, 246, 28, 1, 1, 128, 1776, 4872, 4840, 2136, 427, 36, 1, 1, 216, 4854, 18711, 25107, 15543, 4733, 694, 45, 1, 1, 354, 13184, 70858, 124167, 101538, 43120, 9577, 1071, 55, 1

Offset

1,5

Links

Table of n, a(n) for n=1..66.

Soheir M. Khamis, Height counting of unlabeled interval and N-free posets, Discrete Math. 275 (2004), no. 1-3, 165-175.

Example

Triangle begins:
1
1 1
1 3 1
1 7 6 1
1 13 24 10 1
1 25 77 61 15 1
1 43 228 291 130 21 1
1 76 644 1229 856 246 28 1
1 128 1776 4872 4840 2136 427 36 1
1 216 4854 18711 25107 15543 4733 694 45 1
1 354 13184 70858 124167 101538 43120 9577 1071 55 1
...

Crossrefs

Row sums give A202182. Cf. A202178, A003430, A007453, A053554.

Sequence in context: A284631 A154341 A348863 * A130749 A250118 A250119

Adjacent sequences: A202178 A202179 A202180 * A202182 A202183 A202184

Keyword

nonn,tabl

Author

N. J. A. Sloane, Dec 13 2011

Status

approved