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.

1, 6, 24, 180, 4212, 461064, 302693712

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 * A336267 A018981 A052594

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