Answer
$a_n=4$
Work Step by Step
The formula for finding the arithmetic mean is $\dfrac{x+y}{2}$.
Arithmetic mean is the middle term of any $3$ consecutive terms.
In this sequence the consecutive numbers are $a_{n-1}$, $a_{n}$, and $a_{n+1}$ so the formula is:
$$a_{n}=\dfrac{a_{n-1} + a_{n+1}}{2}$$
Substitute the given values in the formula above to obtain:
$a_{n}=\dfrac{7+1}{2}\\\\$
$a_{n}=4$
