A058561 A 3-way generalization of series-parallel networks with n labeled edges.

0, 1, 3, 12, 78, 708, 8256, 117624, 1980096, 38456736, 846413472, 20819693568, 565998548352, 16852047061632, 545372109629184, 19061178127458816, 715541912895773184, 28713061759257037824, 1226513716981332031488

Offset: 0

Author

N. J. A. Sloane, Dec 26 2000

Keywords

• nonn

Crossrefs

Cf. A058534, A000311, A006351.

Programs

Maple

spec := [ N, {N=Union(Z,S,P,Q), S=Set(Union(Z,P),card>=2), P=Set(Union(Z,Q),card>=2), Q=Set(Union(Z,S),card>=2)}, labeled ]; [seq(combstruct[count](spec,size=n), n=0..40)]; # N = A058561, S=A000311