; This Mathomatic input file contains the formula to
; directly calculate the "n"th Fibonacci number.
; A Fibonacci number is always the sum of the 2 previous Fibonacci numbers.
phi = (1 + (5^(1/2)))/2 ; the golden ratio
fibonacci = ((phi^n) - ((1 - phi)^n))/(5^(1/2))
eliminate phi ; Fibonacci formula:
simplify ; Note that Mathomatic rationalizes the denominator here.
sum n=48 to 49 ; compute the 50th Fibonacci number