Number of distinct ways to erect n semicircles of distinct diameters in [n] on the number line from 1 to 2n using 2 colors where all semicircles of the same color are mutually noncrossing. Two ways are regarded the same if the number line is reversed or the colors are exchanged.

A375254

Number of distinct ways to erect n semicircles of distinct diameters in [n] on the number line from 1 to 2n using 2 colors where all semicircles of the same color are mutually noncrossing. Two ways are regarded the same if the number line is reversed or the colors are exchanged.

Terms

    a(0) =0a(1) =0a(2) =0a(3) =6a(4) =4a(5) =0a(6) =0a(7) =60a(8) =186a(9) =0a(10) =0a(11) =1248a(12) =2590a(13) =0a(14) =0a(15) =22820a(16) =46384a(17) =0a(18) =0a(19) =365392a(20) =730456

External references