(;) Semicolon Math: Counting Stars

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Counting Stars (ID: 16)

Problem status: not solved

Suppose there is a circle with \(15\) evenly spaced points numbered from \(1\) to \(15\) in clockwise order. A star is defined as a sequence five numbers \(a_1, a_2, a_3,a_4,a_5\) with \(a_1 < a_4 < a_2 < a_5 < a_3, 1 \le a_1, a_2, a_3, a_4, a_5 \le 15\) and \(\min(|a_{i + 1} - a_i|, 15 - |a_{i + 1}-a_i|) \ge 2\) for integers \(i\) with \(1\le i \le 5.\) (Let \(a_6 = a_1\).)

Find the number of possible stars.

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