Look at the following matchstick pattern of squares. The squares are not separate. Two neighbouring squares have a common matchstick. Observe the patterns and find the rule that gives the number of matchsticks in terms of the number of squares.

If $x$ varies as $y$, then which of the following is/are correct?

$1. x^2+y^2$ varies as $x^2-y^2$.

$2. \frac{x}{y^2}$ varies inversely as $y$.

$3. \sqrt[n]{x^{2}y}$ varies as $\sqrt[2n]{x^4{y}^2}$.

Select the correct answer using the code given below:

Find the rule which gives the number of matchsticks required to make the following pattern:

A pattern of letter $\mathrm{H}$.