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A064049 Number of possible arrangements of numbers 1 to n*(n+1)/2 in a triangle of n rows so that each row and each diagonal is increasing or decreasing. 2
1, 6, 24, 180, 4212, 461064, 302693712 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..7.

EXAMPLE

The following triangle of 4 rows satisfies the requirements:

....1

...3 2

..4 5 8

.6 7 9 10

CROSSREFS

a(n)=6*A064050(n) for n>1.

Sequence in context: A200904 A293488 A038033 * A018981 A052594 A277985

Adjacent sequences:  A064046 A064047 A064048 * A064050 A064051 A064052

KEYWORD

more,nonn

AUTHOR

Floor van Lamoen, Aug 24 2001

EXTENSIONS

a(7) from Lars Blomberg, Apr 11 2012

STATUS

approved

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Last modified October 22 02:06 EDT 2017. Contains 293756 sequences.