Number of unlabeled series-parallel posets (i.e., generated by unions and sums) with n nodes.

A003430

Number of unlabeled series-parallel posets (i.e., generated by unions and sums) with n nodes.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =5a(4) =15a(5) =48a(6) =167a(7) =602a(8) =2256a(9) =8660a(10) =33958a(11) =135292a(12) =546422a(13) =2231462a(14) =9199869a(15) =38237213a(16) =160047496a(17) =674034147a(18) =2854137769a(19) =12144094756a(20) =51895919734a(21) =222634125803a(22) =958474338539

External references