Number of decomposable fixed-point free involutions, also the number of disconnected chord diagrams with 2n nodes on an open string.
0, 0, 1, 5, 31, 239, 2233, 24725, 318631, 4707359, 78691633, 1471482725
2 seqfan posts
Wed Dec 29 15:36:54 CET 2010 [seqfan] A000698 == indecomposable fixed-point free involutions of {2n}?