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

1,2

Comments

See A339282 for additional details.

Links

Table of n, a(n) for n=1..18.

Example

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).

Prog

(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)) )}

Crossrefs

Row sums of A339282.

Cf. A339225, A339229.

Sequence in context: A165193 A309147 A217903 * A095288 A155105 A132685

Adjacent sequences: A339280 A339281 A339282 * A339284 A339285 A339286

Keyword

nonn

Author

Andrew Howroyd, Nov 30 2020

Status

approved