

A103904


a(n) = n*(n1)/2 * 2^(n*(n1)/2).


5



0, 2, 24, 384, 10240, 491520, 44040192, 7516192768, 2473901162496, 1583296743997440, 1981583836043018240, 4869940435459321626624, 23574053482485268906770432, 225305087149939210031640608768
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OFFSET

1,2


COMMENTS

a(n) is the number of birooted graphs on n labeled nodes.  Andrew Howroyd, Nov 23 2020
Old (incorrect) name was: "Number of perfect matchings of an n X (n+1) Aztec rectangle with the third vertex in the topmost row removed". See Mathematics Stack Exchange for the discussion.  Andrey Zabolotskiy, Jun 05 2022


LINKS



FORMULA



PROG

(PARI) a(n)={binomial(n, 2)*2^binomial(n, 2)} \\ Andrew Howroyd, Nov 23 2020


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS

Name replaced by a formula, a(1) changed from 1 to 0, and entry edited by Andrey Zabolotskiy, Jun 05 2022


STATUS

approved



