NPV = C_0 + \frac{C_1}{1+R} + \frac{C_2}{(1+R)^2} + \frac{C_3}{(1+R)^3} + ... + \frac{C_n}{(1+R)^n}

Where:

C_i is the after tax cashflow in Year i

R is the discount rate 

n is the number of years of cashflow

NPV = \sum^n_0 C_i

Where:

C_i is the after tax cashflow in Year i

n is the number of years of cashflow

NPV = \sum^n_0 \frac{C_i}{n!}

Where:

C_i is the after tax cashflow in Year i

n! is factorial of the number of years of cashflow, n! = 1 * 2 * 3 * ... * n

NPV = \sum^n_0 P_i

Where:

P_i is the after-tax profit in Year i

n is the number of years of profit

NPV = I - \sum^n_0 C_i

Where:

I is the initial investment

C_i is the after tax cashflow in Year i

n is the number of years of cashflow