Question 32
Consider a permutation $(a_{1}, a_{2}, a_{3}, a_{4}, a_{5})$ of $\{1,2,3,4,5\}$. We say the tuple $(a_{1}, a_{2}, a_{3}, a_{4}, a_{5})$ is flawless if for all $1 \leq i\lt j\lt k \leq 5$, the sequence $(a_{i}, a_{j}, a_{k})$ is not an arithmetic progression (in that order). Find the number of flawless 5-tuples.