%I #9 Sep 02 2017 15:50:04

%S 1,2,9,61,449,3161,21145,136529,862209,5369617,33133481,203119577,

%T 1239049729,7528608985,45596026169,275385806881,1659295498241,

%U 9977108934689,59881303252297,358815987469673,2146943650081281,12829239786138217,76571416493573849,456525052642949681

%N The order of the semigroup of orientation-preserving partial transformations on n elements.

%C Row sums of A289710 and of A289711.

%H A. Umar, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL14/Umar/umar2.html">Combinatorial Results for Semigroups of Orientation-Preserving Partial Transformations</a>, J. Int. Seq. 14 (2011) # 11.7.5, Tables 2.1, 2.2 and 2.3.

%Y Cf. A289710, A289711.

%K nonn,easy

%O 0,2

%A _R. J. Mathar_, Sep 02 2017