MathDB

A rectangular

1

10

strip is divided into

10

1

1

squares. The numbers

1

2

3

...

10

are placed in the squares in the following way. First the number

1

is placed in an arbitrary square, then

2

is placed in a neighbouring square, then

3

is placed into a free square neighbouring one of the squares occupied earlier, and so on (up to

10

). How many different permutations of

1

2

3

...

10

can one get in this way?
(A Shen)

Problem Statement