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A373115
Number weak ascent sequences of length 2n (prefixed with a zero) with exactly n weak ascents.
2
1, 0, 0, 1, 35, 1661, 107002, 9047970, 972937247, 129603346139, 20934881571217, 4029204458109445, 910549073414709876, 238643240329544375336, 71772700696174395158056, 24544642886642172762170933, 9468192975202745545226891834, 4090995487728206638560153282674
OFFSET
0,5
LINKS
Beata Benyi, Anders Claesson, and Mark Dukes, Weak ascent sequences and related combinatorial structures, arXiv:2111.03159 [math.CO], 2021-2022.
FORMULA
a(n) = A369321(2n,n).
MAPLE
b:= proc(n, i, t) option remember; expand(`if`(n=0, 1, add(
b(n-1, j, t+`if`(j>=i, 1, 0))*`if`(j>=i, x, 1), j=0..t+1)))
end:
a:= n-> coeff(b(2*n, -1$2), x, n):
seq(a(n), n=0..17);
CROSSREFS
Sequence in context: A180883 A130005 A199362 * A187364 A183417 A199587
KEYWORD
nonn
AUTHOR
Alois P. Heinz, May 25 2024
STATUS
approved