You are right click it lol!
Answer is n^2+2
I attached a picture of my working out
The sum clearly diverges. This is indisputable. The point of the claim above, that

is to demonstrate that a sum of infinitely many terms can be manipulated in a variety of ways to end up with a contradictory result. It's an artifact of trying to do computations with an infinite number of terms.
The mathematician Srinivasa Ramanujan famously demonstrated the above as follows: Suppose the series converges to some constant, call it

. Then

Now, recall the geometric power series

which holds for any

. It has derivative

Taking

, we end up with

and so

But as mentioned above, neither power series converges unless

. What Ramanujan did was to consider the sum

as a limit of the power series evaluated at

:

then arrived at the conclusion that

.
But again, let's emphasize that this result is patently wrong, and only serves to demonstrate that one can't manipulate a sum of infinitely many terms like one would a sum of a finite number of terms.
Plot and connect the points A(6,-7), B(1,-7), C(1,-4), D(3,-2), E(7,-2), F(7,-4), and find the length of DE
strojnjashka [21]
The length is 4 units...
They share the same value of y so the length would be | 7 - 3 | = 4