What is a sequence?

The largest common term to the sequences $1, 11, 21, 31, ....100$ terms and $31, 36, 41, 45, 46....100$ terms is

If the sum of first four terms of an $\mathrm{AP}$ is $40$ and that of first $14$ terms is $280$. Find the sum of its first $\mathrm{n}$ terms.

If $1^2 + 2^2 + 3^2 + ...... + {10}^2 = 385$, then the value of $2^2 + 4^2 + 6^2 + ..... + {20}^2$ will be _____.