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A355172
The Fuss-Catalan triangle of order 2, read by rows. Related to ternary trees.
3
1, 0, 1, 0, 1, 3, 0, 1, 5, 12, 0, 1, 7, 25, 55, 0, 1, 9, 42, 130, 273, 0, 1, 11, 63, 245, 700, 1428, 0, 1, 13, 88, 408, 1428, 3876, 7752, 0, 1, 15, 117, 627, 2565, 8379, 21945, 43263, 0, 1, 17, 150, 910, 4235, 15939, 49588, 126500, 246675
OFFSET
0,6
COMMENTS
The Fuss-Catalan triangle of order m is a regular, (0, 0)-based table recursively defined as follows: Set row(0) = [1] and row(1) = [0, 1]. Now assume row(n-1) already constructed and duplicate the last element of row(n-1). Next apply the cumulative sum m times to this list to get row(n). Here m = 2. (See the Python program for a reference implementation.)
This definition also includes the Fuss-Catalan numbers A001764(n) = T(n, n), or row 3 in A355262. For m = 1 see A355173 and for m = 3 A355174. More generally, for n >= 1 all Fuss-Catalan sequences (A355262(n, k), k >= 0) are the main diagonals of the Fuss-Catalan triangles of order n - 1.
FORMULA
The general formula for the Fuss-Catalan triangles is, for m >= 0 and 0 <= k <= n:
FCT(n, k, m) = (m*(n - k) + m + 1)*(m*n + k - 1)!/((m*n + 1)!*(k - 1)!)) for k > 0 and FCT(n, 0, m) = 0^n. The case considered here is T(n, k) = FCT(n, k, 2).
T(n, k) = (2*n - 2*k + 3)*(2*n + k - 1)!/((2*n + 1)!*(k - 1)!) for k > 0; T(n, 0) = 0^n.
The g.f. of row n of the FC-triangle of order m is 0^n + (x - (m + 1)*x^2) / (1 - x)^(m*n + 2), thus:
T(n, k) = [x^k] (0^n + (x - 3*x^2)/(1 - x)^(2*n + 2)).
EXAMPLE
Table T(n, k) begins:
[0] [1]
[1] [0, 1]
[2] [0, 1, 3]
[3] [0, 1, 5, 12]
[4] [0, 1, 7, 25, 55]
[5] [0, 1, 9, 42, 130, 273]
[6] [0, 1, 11, 63, 245, 700, 1428]
[7] [0, 1, 13, 88, 408, 1428, 3876, 7752]
.
Seen as an array reading the diagonals starting from the main diagonal:
[0] 1, 1, 3, 12, 55, 273, 1428, 7752, 43263, 246675, ... A001764
[1] 0, 1, 5, 25, 130, 700, 3876, 21945, 126500, 740025, ... A102893
[2] 0, 1, 7, 42, 245, 1428, 8379, 49588, 296010, 1781325, ... A102594
[3] 0, 1, 9, 63, 408, 2565, 15939, 98670, 610740, 3786588, ... A230547
[4] 0, 1, 11, 88, 627, 4235, 27830, 180180, 1157013, 7396972, ...
PROG
(Python)
from functools import cache
from itertools import accumulate
@cache
def Trow(n: int) -> list[int]:
if n == 0: return [1]
if n == 1: return [0, 1]
row = Trow(n - 1) + [Trow(n - 1)[n - 1]]
return list(accumulate(accumulate(row)))
for n in range(9): print(Trow(n))
CROSSREFS
A001764 (main diagonal), A102893 (subdiagonal), A102594 (diagonal 2), A230547 (diagonal 3), A005408 (column 2), A071355 (column 3), A006629 (row sums), A143603 (variant).
Cf. A123110 (triangle of order 0), A355173 (triangle of order 1), A355174 (triangle of order 3), A355262 (Fuss-Catalan array).
Sequence in context: A046778 A119925 A210663 * A102765 A355257 A129684
KEYWORD
nonn,tabl
AUTHOR
Peter Luschny, Jun 25 2022
STATUS
approved