A202179 Triangle read by rows: T(n,k) = number of n-element unlabeled connected N-free posets of height k (2 <= k <= n).

1, 2, 1, 3, 5, 1, 4, 17, 9, 1, 5, 45, 50, 14, 1, 6, 115, 218, 114, 20, 1, 7, 278, 851, 709, 224, 27, 1, 8, 679, 3161, 3818, 1867, 398, 35, 1, 9, 1666, 11507, 19042, 13113, 4276, 657, 44, 1, 10, 4167, 41837, 91383, 83222, 37898, 8845, 1025, 54, 1

Offset

2,2

Links

Table of n, a(n) for n=2..56.

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
2 1
3 5 1
4 17 9 1
5 45 50 14 1
6 115 218 114 20 1
7 278 851 709 224 27 1
8 679 3161 3818 1867 398 35 1
9 1666 11507 19042 13113 4276 657 44 1
10 4167 41837 91383 83222 37898 8845 1025 54 1
...

Crossrefs

See A202178 for another version. Row sums give A202180.

Sequence in context: A337886 A337884 A337883 * A297519 A297749 A173588

Adjacent sequences: A202176 A202177 A202178 * A202180 A202181 A202182

Keyword

nonn,tabl

Author

N. J. A. Sloane, Dec 13 2011

Status

approved