A221529 Triangle read by rows: T(n,k) = A000203(k)*A000041(n-k), 1 <= k <= n.
1, 1, 3, 2, 3, 4, 3, 6, 4, 7, 5, 9, 8, 7, 6, 7, 15, 12, 14, 6, 12, 11, 21, 20, 21, 12, 12, 8, 15, 33, 28, 35, 18, 24, 8, 15, 22, 45, 44, 49, 30, 36, 16, 15, 13, 30, 66, 60, 77, 42, 60, 24, 30, 13, 18, 42, 90, 88, 105, 66, 84, 40, 45, 26, 18, 12, 56, 126, 120, 154, 90, 132, 56, 75, 39, 36, 12, 28
Offset: 1
Examples
Triangle begins:
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n| k 1 2 3 4 5 6 7 8 9 10
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1| 1;
2| 1, 3;
3| 2, 3, 4;
4| 3, 6, 4, 7;
5| 5, 9, 8, 7, 6;
6| 7, 15, 12, 14, 6, 12;
7| 11, 21, 20, 21, 12, 12, 8;
8| 15, 33, 28, 35, 18, 24, 8, 15;
9| 22, 45, 44, 49, 30, 36, 16, 15, 13;
10| 30, 66, 60, 77, 42, 60, 24, 30, 13, 18;
...
The sum of row 10 is [30 + 66 + 60 + 77 + 42 + 60 + 24 + 30 + 13 + 18] = A066186(10) = 420.
.
For n = 10 the calculation of the row 10 is as follows:
k A000203 T(10,k)
1 1 * 30 = 30
2 3 * 22 = 66
3 4 * 15 = 60
4 7 * 11 = 77
5 6 * 7 = 42
6 12 * 5 = 60
7 8 * 3 = 24
8 15 * 2 = 30
9 13 * 1 = 13
10 18 * 1 = 18
A000041
.
From _Omar E. Pol_, Jul 13 2021: (Start)
For n = 10 we can see below three views of two associated polycubes called here "prism of partitions" and "tower". Both objects contain the same number of cubes (that property is valid for n >= 1).
_ _ _ _ _ _ _ _ _ _
42 |_ _ _ _ _ |
|_ _ _ _ _|_ |
|_ _ _ _ _ _|_ |
|_ _ _ _ | |
|_ _ _ _|_ _ _|_ |
|_ _ _ _ | |
|_ _ _ _|_ | |
|_ _ _ _ _|_ | |
|_ _ _ | | |
|_ _ _|_ | | |
|_ _ | | | |
|_ _|_ _|_ _|_ _|_ | _
30 |_ _ _ _ _ | | | | 30
|_ _ _ _ _|_ | | | |
|_ _ _ | | | | |
|_ _ _|_ _ _|_ | | | |
|_ _ _ _ | | | | |
|_ _ _ _|_ | | | | |
|_ _ _ | | | | | |
|_ _ _|_ _|_ _|_ | | _|_|
22 |_ _ _ _ | | | | | 22
|_ _ _ _|_ | | | | |
|_ _ _ _ _|_ | | | | |
|_ _ _ | | | | | |
|_ _ _|_ | | | | | |
|_ _ | | | | | | |
|_ _|_ _|_ _|_ | | | _|_ _|
15 |_ _ _ _ | | | | | | | 15
|_ _ _ _|_ | | | | | | |
|_ _ _ | | | | | | | |
|_ _ _|_ _|_ | | | | _|_|_ _|
11 |_ _ _ | | | | | | | | 11
|_ _ _|_ | | | | | | | |
|_ _ | | | | | | | | |
|_ _|_ _|_ | | | | | _| |_ _ _|
7 |_ _ _ | | | | | | | | | 7
|_ _ _|_ | | | | | | _|_ _|_ _ _|
5 |_ _ | | | | | | | | | | | 5
|_ _|_ | | | | | | | _| | |_ _ _ _|
3 |_ _ | | | | | | | | _|_ _|_|_ _ _ _| 3
2 |_ | | | | | | | | | _ _|_ _|_|_ _ _ _ _| 2
1 |_|_|_|_|_|_|_|_|_|_| |_ _|_|_|_ _ _ _ _ _| 1
.
Figure 1. Figure 2.
Front view of the Lateral view
prism of partitions. of the tower.
.
. _ _ _ _ _ _ _ _ _ _
| | | | | | | | |_| 1
| | | | | | |_|_ _| 2
| | | | |_|_ |_ _| 3
| | |_|_ |_ _ _| 4
| |_ _ |_ |_ _ _| 5
|_ _ |_ |_ _ _ _| 6
|_ | |_ _ _ _| 7
|_ |_ _ _ _ _| 8
| | 9
|_ _ _ _ _ _| 10
.
Figure 3.
Top view
of the tower.
.
Figure 1 is a two-dimensional diagram of the partitions of 10 in colexicographic order (cf. A026792, A211992). The area of the diagram is 10*42 = A066186(10) = 420. Note that the diagram can be interpreted also as the front view of a right prism whose volume is 1*10*42 = 420 equaling the volume and the number of cubes of the tower that appears in the figures 2 and 3.
Note that the shape and the area of the lateral view of the tower are the same as the shape and the area where the 1's are located in the diagram of partitions. In this case the mentioned area equals A000070(10-1) = 97.
The connection between these two associated objects is a representation of the correspondence divisor/part described in A338156. See also A336812.
The sum of the volumes of both objects equals A220909.
For the connection with the table of A338156 see also A340035. (End)
Links
- Paolo Xausa, Table of n, a(n) for n = 1..11325 (rows 1..150 of triangle, flattened)
- T. J. Osler, A. Hassen and T. R. Chandrupatia, Surprising connections between partitions and divisors, The College Mathematics Journal, Vol. 38. No. 4, Sep. 2007, 278-287 (see p. 287).
- Omar E. Pol, Illustration of the prism, the tower and the 10th row of the triangle
Programs
-
Mathematica
nrows=12; Table[Table[DivisorSigma[1,k]PartitionsP[n-k],{k,n}],{n,nrows}] // Flatten (* Paolo Xausa, Jun 17 2022 *) -
PARI
T(n,k)=sigma(k)*numbpart(n-k) \\ Charles R Greathouse IV, Feb 19 2013
Comments