A339226 Number of oriented series-parallel networks with n elements of 2 colors.

2, 7, 32, 176, 1066, 6935, 47216, 332700, 2404818, 17734668, 132901644, 1009161505, 7747608480, 60037905076, 468987635982, 3689066578347, 29195587558726, 232303316402615, 1857264782113562, 14912673794505898, 120203145484455930, 972291038495626309

Offset: 1

Author

Andrew Howroyd, Nov 28 2020

Keywords

• nonn

Comments

See A339228 for additional details.

Examples

			In the following examples elements in series are juxtaposed and elements in parallel are separated by '|'.
a(1) = 2: (1), (2).
a(2) = 7: (11), (12), (21), (22), (1|1), (1|2), (2|2).
		

Crossrefs

Cf. A003430, A339227, A339228.

Programs

PARI

\\ See A339228 for R(n,k).
seq(n) = {R(n,2)}