A339280 Number of unoriented series-parallel networks with n elements of 2 colors.

2, 6, 22, 106, 582, 3622, 24060, 167803, 1206852, 8881775, 66496238, 504729590, 3874281594, 30020527274, 234498941338, 1844550287865, 14597849688004, 116151844649673, 928633009522942, 7456338969251761, 60101579662366508, 486145542528043029, 3944844113529346468

Offset

1,1

Comments

See A339282 for additional details.

Links

Table of n, a(n) for n=1..23.

Example

In the following examples, elements in series are juxtaposed and elements in parallel are separated by '|'.
a(1) = 2: (1), (2).
a(2) = 6: (11), (12), (22), (1|1), (1|2), (2|2).

Prog

(PARI) \\ See A339282 for R(n, k).
seq(n) = {R(n, 2)}

Crossrefs

Cf. A339225, A339226, A339281, A339282.

Sequence in context: A103941 A064643 A218531 * A129535 A216720 A174074

Adjacent sequences: A339277 A339278 A339279 * A339281 A339282 A339283

Keyword

nonn

Author

Andrew Howroyd, Nov 30 2020

Status

approved