Observe the given pattern.
The number of white squares in
1. first figure = $$1\times1 - 0\times0 = 1$$
2. second figure = $$2\times2 - 1\times1 = 3$$
3. third figure = $$3\times3 - 2\times2 = 5$$
4. fourth figure = $$4\times4 - 3\times3 = 7$$
Similarly, what is the number of white squares in the 7th pattern?