For a positive integer n, (1 + 1/x)^n is expanded in increasing powers of x. If three consecutive coefficients

Question

For a positive integer n, $\left(1+{1\over x}\right)^n$ is expanded in increasing powers of x. If three consecutive coefficients in this expansion are in the ratio, 2 : 5 : 12 , then n is equal to _______

Numerical Value Type