Number of ways of arranging n chords on a circle (handshakes between 2n people across a table) with exactly 2 simple intersections.

A074922

Number of ways of arranging n chords on a circle (handshakes between 2n people across a table) with exactly 2 simple intersections.

Terms

    a(0) =0a(1) =0a(2) =0a(3) =3a(4) =28a(5) =180a(6) =990a(7) =5005a(8) =24024a(9) =111384a(10) =503880a(11) =2238390a(12) =9806280a(13) =42493880a(14) =182530530a(15) =778439025a(16) =3300049200a(17) =13919756400a(18) =58462976880a(19) =244639718730

External references