124
The given series is based on the following pattern :
$latex 1^{3}-1 = 0$
$latex 2^{3}-1 = 7$
$latex 3^{3}-1 = 26$
$latex 4^{3}-1 = 63$
$latex 5^{3}-1 = \underline{124}$
$latex 6^{3}-1 = 215$
$latex 7^{3}-1 = 352$
Hence the missing term is 124.