MathDB
Integers in a Grid

Source: 2023 AIME II/10

February 16, 2023
AMCAIME

Problem Statement

Let NN be the number of ways to place the integers 11 through 1212 in the 1212 cells of a 2×62\times 6 grid so that for any two cells sharing a side, the difference between the numbers in those cells is not divisible by 33. One way to do this is shown below. Find the number of positive integer divisors of NN.
[asy] size(160); defaultpen(linewidth(0.6)); for(int j=0;j<=6;j=j+1) { draw((j,0)--(j,2)); } for(int i=0;i<=2;i=i+1) { draw((0,i)--(6,i)); } for(int k=1;k<=12;k=k+1) { label(""+((string)k)+""+((string) k)+"",(floor((k-1)/2)+0.5,k%2+0.5)); } [/asy]