1. Which formula we must apply, in order to calculate the number of dots in 7th figure?
2. How many dots are there in the 27th figure?

We can see that in order to shape the next figure we add up consecutively 4, 6, 8, 10, 12, 14, ……………… dots.

So, the 5th figure will consist of 20+10 = 30 dots, 6th will consist of 30+12=42 dots and 7th figure will consist of 42+14 = 56 dots.

Also, we can notice that every figure consists of a square that has in each side the same number of dots as the number of order of figure, plus one more column.

Therefore, this is the formula we need in order to calculate the number of dots in anyone figure of this sequence.

So, the 27th figure will consists of 27 2 + 27 = 756 dots.