Answer
$a_n=n^2-1$
Work Step by Step
$a_1=0=1^2-1$
$a_2=3=2^2-1$
$a_3=8=3^2-1$
$a_4=15=4^2-1$
$a_5=24=5^2-1$
Each term is 1 less than the square of $n$: $a_n=n^2-1$
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