Inserting 3 arithmetic means between 5 and 17 makes an arithmetic sequence with 5 as the first term and 17 as the fifth term. Solve for the common difference by,
d = (a5 - a1) / (5 - 1)
d = (17 - 5) / (5 - 1) = 3
Then the terms are calculated by the equation,
an = a1 + (n - 1) x d
From this, the value of the arithmetic means are 8, 11, and 14.