2

Part of 2022 Girls in Math at Yale

Problems(1)

Girls in Math at Yale 2022 Problem 2: Filling In Grid

Source:

How many ways are there to fill in a

2\times 2

square grid with the numbers

1,2,3,

4

such that the numbers in any two grid squares that share an edge have an absolute difference of at most

2

?
Proposed by Andrew Wu