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A173997 Irregular triangular by columns derived from (1, 2, 3,...) * (1, 2, 3,...). 2
1, 2, 3, 2, 4, 4, 5, 6, 3, 6, 8, 6, 7, 10, 9, 4, 8, 12, 12, 8, 9, 14, 15, 12, 5, 10, 16, 18, 16, 10, 11, 18, 21, 20, 15, 6, 12, 20, 24, 24, 20, 12 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Row sums = A006918: (1, 2, 5, 8, 14, 20, 30,...).

LINKS

Table of n, a(n) for n=1..42.

FORMULA

Given a (1, 2, 3,...) * (1, 2, 3,...) multiplication table; leftmost column

of the triangle = (1, 2, 3,...). Then shift down each successive column of

the array twice to get triangle A173997.

EXAMPLE

Given:

...

1,..2,..3,..4,..5,...

2,..4,..6,..8,.10,...

3,..6,..9,.12,.15,...

4,..8,.12,.16,.20,...

...

After the shift twice operation, we obtain:

...

1;

2;

3, 2;

4, 4;

5, 6, 3;

6, 8, 6;

7, 10, 9, 4;

8, 12, 12, 8;

9, 14, 15, 12, 5;

10, 16, 18, 16, 10;

11, 18, 21, 20, 15, 6;

12, 20, 24, 24, 20, 12;

...

CROSSREFS

Cf. A006918

Sequence in context: A145394 A179806 A182762 * A029143 A153846 A284383

Adjacent sequences:  A173994 A173995 A173996 * A173998 A173999 A174000

KEYWORD

nonn,tabf

AUTHOR

Gary W. Adamson, Mar 05 2010

STATUS

approved

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Last modified February 19 10:18 EST 2019. Contains 320310 sequences. (Running on oeis4.)