Given Sequence is $0,7,26,63,\dots$
We've to find the next number after $63$
Observe the following
$0 = 1^3 - 1$
$7 = 2^3-1$
$26 = 3^3 - 1$
$63 = 4^3-1$
$\therefore$ Next number will be $(5^3-1)$ i.e. $(125-1) =124$
The sequence will be $0,7,26,63,124,215,342,511,728,999,\dots$