You can do it by setting up an equation for the nth term of a sequence.

The "general term", of a sequence will be compared to the placement of the numbers in the sequence, .

As sequence increases at a rate of , , where is an unknown integer that we still need to work out. When , . Substituting this into the equation gives , so and the equation I was looking for is . You can check this by substituting in the other numbers of the sequence. Ie, when is , does ?

If you do the same for the bottom sequence, then you have two simultaneous equations. You need to solve these for .