Answer
$a_1=2$
$a_2=4$
$a_3=12$
$a_4=48$
Work Step by Step
$a_1=2$
$a_2=2\times a_1=2\times 2=4$
$a_3=3\times a_2=3\times 4=12$
$a_4=4\times a_3=4\times 12=48$
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