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A361245
Number of noncrossing 2,3 cacti with n nodes.
7
1, 1, 1, 4, 20, 115, 715, 4683, 31824, 222300, 1586310, 11514030, 84742320, 630946446, 4743789260, 35965715780, 274659794160, 2110810059795, 16312695488265, 126693445737170, 988340783454380, 7740875273884445, 60846920004855985, 479854293574853085
OFFSET
0,4
COMMENTS
A 2,3 cactus is a cactus composed of bridges and triangles.
PROG
(PARI) seq(n) = Vec(1 + x/(1 - serreverse((sqrt(1 + 4*x + O(x^n)) - 1)*(1 - x)^2/2)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Mar 08 2023
STATUS
approved