A355172 The Fuss-Catalan triangle of order 2, read by rows. Related to ternary trees.
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
Examples
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, ...
Crossrefs
Programs
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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))
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)).
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