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A339283 Number of unoriented series-parallel networks with n integer valued elements spanning an initial interval of positive integers. 3
1, 4, 28, 361, 7061, 184327, 5941855, 226973560, 10011116097, 500553647373, 27975194135702, 1728193768303770, 116934429186262096, 8600448307248025405, 683181845460624644202, 58290243136791332908001, 5316517137637684870655592, 516199318599186277653647746 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 21 12:54 EDT 2021. Contains 347598 sequences. (Running on oeis4.)