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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
OFFSET
1,2
COMMENTS
See A339282 for additional details.
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.
Sequence in context: A165193 A309147 A217903 * A095288 A155105 A132685
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Nov 30 2020
STATUS
approved