A283367 Irregular triangle read by rows: T(n,k) = number of horizontal positions for the vertical legs of the Dyck paths for the symmetric representation of sigma(n) that are listed in the corresponding positions of the triangle of A259177.

1, 2, 2, 3, 3, 4, 3, 5, 4, 5, 6, 4, 5, 7, 5, 6, 8, 5, 7, 9, 6, 7, 8, 10, 6, 7, 8, 11, 7, 9, 10, 12, 7, 9, 10, 13, 8, 9, 11, 14, 8, 10, 11, 12, 15, 9, 11, 12, 13, 16, 9, 11, 12, 13, 17, 10, 12, 13, 15, 18, 10, 12, 13, 15, 19, 11, 13, 15, 16, 20, 11, 14, 15, 16, 17, 21

Offset

1,2

Comments

The dot product of the n-th row of this triangle and the n-th row of triangle A259177 equals A024916(n), the sum of all divisors of numbers 1 through n (true for all n <= 20000); the value of a(n) is the sum of the rectangles between the y-axis and the vertical legs of the symmetric representation of sigma(n). This is the companion computation to A283368.

Links

Table of n, a(n) for n=1..76.

Formula

T(n,k) = sum_{i=1..k} f(n, 2*i-1) where f is defined in A237593.

A024916(n) = sum_{i=1..row(n)} (T(n,i))*S(n,i)) where S(n,i) refers to the triangle of A259177 and row(n) = floor(sqrt(8*n+1)-1)/2).

Example

The first vertical leg of the symmetric representation of sigma(15) is at x-coordinate 8 and has length 3, and row 15 has 5 entries so that T(15,1) = 8 and T(15,5) = 15.
The first 16 rows of the irregular triangle:
1:   1
2:   2
3:   2    3
4:   3    4
5:   3    5
6:   4    5    6
7:   4    5    7
8:   5    6    8
9:   5    7    9
10:   6    7    8   10
11:   6    7    8   11
12:   7    9   10   12
13:   7    9   10   13
14:   8    9   11   14
15:   8   10   11   12   15
16:   9   11   12   13   16

Mathematica

(* function f[n, k] and its support functions are defined in A237593 *)
a283367[n_, k_] := Sum[f[n, 2*i-1], {i, k}]
TableForm[Table[a283367[n, k], {n, 1, 16}, {k, 1, row[n]}]] (* triangle *)
Flatten[Table[a283367[n, k], {n, 1, 21}, {k, 1, row[n]}]] (* sequence data *)

Crossrefs

Cf. A024916, A237593, A259176, A259177, A283368.

Sequence in context: A323636 A375115 A375110 * A322528 A258756 A127431

Adjacent sequences: A283364 A283365 A283366 * A283368 A283369 A283370

Keyword

nonn,tabf

Author

Hartmut F. W. Hoft, Mar 06 2017

Status

approved