Problem

Source: (2021-) 2022 XV 15th Dürer Math Competition Finals Day 2 E+1

Tags: Digits, number theory



How many $10$-digit sequences are there, made up of $1$ four, $2$ threes, $3$ twos, and $4$ ones, in which there is a two in between any two ones, a three in between any two twos, and a four in between any two threes?