Given Sequence is $0,7,26,63,.......$

We've to find the next number after $63$

Observe the following

$0 = 1^3 - 1$

$7 = 2^3-1$

$26 = 3^3 - 1$

$63 = 4^3-1$

$\color{green}{\text{∴Next number will be}}$ $\color{maroon}{(5^3-1)}$ i.e. $(125-1) = \color{purple}{124}$

$\color{gold}{\text{The sequence will be}}$ $\color{blue}{0,7,26,63,124,215,342,511,728,999,.....}$