A283368 - OEIS

A283368

Irregular triangle read by rows: T(n,k) = number of heights for the horizontal elements of the Dyck paths for the symmetric representation of sigma(n) that are listed in the corresponding positions of the triangle of A259176.

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

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OFFSET

1,2

COMMENTS

The dot product of the n-th row of this triangle and the n-th row of triangle A259176 equals A024916(n), the sum of all divisors of numbers 1 through n (true for all n <= 20000); the value is the sum of the rectangles between the x-axis and the horizontal legs of the symmetric representation of sigma(n). This is the companion computation to A283367.

LINKS

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

FORMULA

T(n,k) = n - sum_{i=1..k-1} f(n, 2*i) 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 A259176 and row(n) = floor(sqrt(8*n+1)-1)/2).

EXAMPLE

The first horizontal leg of the symmetric representation of sigma(15) is at y-coordinate 15 and has length 8, and row 15 has 5 entries so that T(15,1) = 15 and T(15,5) = 8.

The first 16 rows of the irregular triangle:

3 2

4 3

5 3

6 5 4

7 5 4

8 6 5

9 7 5

10 8 7 6

11 8 7 6

12 10 9 7

13 10 9 7

14 11 9 8

15 12 11 10 8

16 13 12 11 9

MATHEMATICA

(* function f[n, k] and its support functions are defined in A237593 *)

a283368[n_, k_] := n - Sum[f[n, 2i], {i, k-1}]

TableForm[Table[a283368[n, k], {n, 1, 16}, {k, 1, row[n]}]] (* triangle *)

Flatten[Table[a283368[n, k], {n, 1, 21}, {k, 1, row[n]}]] (* sequence data *)

CROSSREFS

Cf. A024916, A237593, A259176, A259177, A283367.

Sequence in context: A331253 A264116 A361000 * A199474 A246694 A054384

Adjacent sequences: A283365 A283366 A283367 * A283369 A283370 A283371

KEYWORD

nonn,tabf

AUTHOR

Hartmut F. W. Hoft, Mar 06 2017

STATUS

approved