A006350 Related to series-parallel networks.

0, 1, 7, 27, 101, 337, 1151, 3843, 12965, 43773, 148529, 505605, 1727771, 5920823, 20345445, 70073901, 241849929, 836230109, 2896104951, 10044664507, 34884102385, 121293088909, 422196245641, 1471030361069, 5130057477187, 17905427995239

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• easy

References

• Z. A. Lomnicki, Two-terminal series-parallel networks, Adv. Appl. Prob., 4 (1972), 109-150.
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A000084, A006349, A058351, A058352, A058353, A000669.

Formula

Sum_{k=1..n-1} A000084(k)*A006349(n-k), n >= 2.