A339283 Number of unoriented series-parallel networks with n integer valued elements spanning an initial interval of positive integers.

1, 4, 28, 361, 7061, 184327, 5941855, 226973560, 10011116097, 500553647373, 27975194135702, 1728193768303770, 116934429186262096, 8600448307248025405, 683181845460624644202, 58290243136791332908001, 5316517137637684870655592, 516199318599186277653647746

Offset: 1

Author

Andrew Howroyd, Nov 30 2020

Keywords

• nonn

Comments

See A339282 for additional details.

Examples

			In the following examples, elements in series are juxtaposed and elements in parallel are separated by '|'.
a(1) = 1: (1).
a(2) = 4: (11), (12), (1|1), (1|2).
		

Crossrefs

Row sums of A339282.

Cf. A339225, A339229.

Programs

PARI

\\ See A339282 for R(n,k).
seq(n)={sum(k=1, n, R(n, k)*sum(r=k, n, binomial(r, k)*(-1)^(r-k)) )}