A332651 - OEIS

%I #10 Dec 23 2020 01:51:45

%S 1,1,0,0,1,0,1,1,1,1,4,2,7,9,14,26,48,71,154,243,478,894,1631,3149,

%T 6062,11295,22469,42900,83528,164829,321012,632960,1255613,2472803,

%U 4928140,9808439,19533534,39134059,78345317,157177556,316398963,636790282,1284910954

%N Number of polygonal cacti on n unlabeled nodes with every polygon having an even number of edges.

%C Bridges are disallowed.

%H Andrew Howroyd, <a href="/A332651/b332651.txt">Table of n, a(n) for n = 0..200</a>

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Cactus_graph">Cactus graph</a>

%H <a href="/index/Ca#cacti">Index entries for sequences related to cacti</a>

%e a(6) = 1 corresponding with a hexagon.

%e a(7) = 1 corresponding with two quadrilaterals joined at a node.

%o (PARI) \\ See A332650 for UCacti.

%o seq(n)={concat([1], UCacti(vector(n, i, i>2&&i%2==0)))}

%Y Cf. A000083, A035085, A091487, A332649, A332650.

%K nonn

%O 0,11

%A _Andrew Howroyd_, Feb 18 2020