Connected Permutation Lists of Integers

1550AdeptCombinatoricsCounting Principles

AMC 12B · 2012 · Problem 18

Let $(a_1,a_2, \dots ,a_{10})$ be a list of the first $10$ positive integers such that for each $2 \le i \le 10$ either $a_i+1$ or $a_i-1$ or both appear somewhere before $a_i$ in the list. How many such lists are there?

Answer choices

120

512

1024

181,440

362,880

0 students attempted0% solvedRating 1550

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