A339229 Number of oriented series-parallel networks with n integer valued elements spanning an initial interval of positive integers.

1, 5, 46, 677, 13897, 367329, 11875112, 453884998, 20021744482, 1001103144204, 55950350379398, 3456387167052662, 233868854544617505, 17200896572547662922, 1366363690436820691346, 116580486267706011046208, 10633034275200701222560393, 1032398637197381396948606128

Offset

1,2

Comments

See A339228 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) = 5: (11), (12), (21), (1|1), (1|2).

Prog

(PARI) \\ See A339228 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 A339228.

Sequence in context: A052894 A363355 A292408 * A295552 A066998 A036246

Adjacent sequences: A339226 A339227 A339228 * A339230 A339231 A339232

Keyword

nonn

Author

Andrew Howroyd, Nov 28 2020

Status

approved