login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A366920
a(n) is the number times a Dyck path in an m X m box of any size has area n, counted to the lower right.
0
1, 1, 0, 1, 1, 0, 1, 2, 1, 1, 1, 3, 3, 3, 2, 2, 5, 6, 7, 7, 5, 6, 8, 12, 15, 18, 16, 16, 15, 17, 24, 32, 40, 43, 45, 45, 42, 44, 53, 69, 87, 104, 115, 126, 125, 124, 124, 136, 160, 198, 240, 282, 321, 345, 360, 365, 367, 382, 417, 482, 574, 682, 791, 895, 976
OFFSET
0,8
COMMENTS
A Dyck path in an m X m grid is a set of up steps U and right steps R from the lower left corner to the upper right corner, staying weakly above the diagonal.
For this statistic, count the boxes below and to the right of the path.
The first time an area appears in two different squares is at size 15, which appears in the 4 X 4 box below UUURURRR and in the 5 X 5 box below URURURURUR.
FORMULA
G.f.: 1 + q + q^3 + q^4 + q^6 + 2q^7 + ...
To construct the g.f., take A(x,q) as defined in A227543, and replace each instance of x^k with q^(k*(k+1)/2).
EXAMPLE
The 0 X 0 box yields the trivial (empty) path of area 0.
The 1 X 1 box yields one Dyck path of area 1 (UR).
The 2 X 2 box yields one Dyck path each of area 3 (URUR) and 4 (UURR).
The 3 X 3 box yields one Dyck path of area 6 (URURUR), two of area 7 (UURRUR and URUURR), and one each of area 8 (UURURR) and 9 (UUURRR).
CROSSREFS
Sequence in context: A047100 A124772 A227543 * A374932 A344678 A079415
KEYWORD
nonn
AUTHOR
William J. Keith, Oct 28 2023
EXTENSIONS
a(45)-a(65) from Alois P. Heinz, Oct 29 2023
STATUS
approved