Number of series-parallel networks with n unlabeled edges. Also called yoke-chains by Cayley and MacMahon.
1, 2, 4, 10, 24, 66, 180, 522, 1532, 4624, 14136, 43930, 137908, 437502, 1399068
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Fri Oct 29 05:35:16 CEST 2010 [seqfan] Implementing first 500 sequences in Java