This video shows that sum of all natural numbers can be represented as an infinite geometric series of all the powers of 9:1+2+3+4+... = 1+9+81+729+...Then this formula for an infinite geometric series is applied:1/(1-x) = 1+x+x^2+x^3+x^4+...and the result1+2+3+4+...= -1/8is demonstrated again.