UPDATED: After realizing that very large Fibonacci numbers would not work with my formula, I went about it a bit differently. This time I created a while loop tied to the input being smaller than the last element in my fib array, creating a Fibonacci sequence where fib[-1] should == i if i is in fact fibonacci. This seemed like a more roundabout…

Scamming the system!!

def is_fibonacci?(i)
  fib = [0,1]
	while i > fib[-1]
		fib << (fib[-1] + fib[-2])
	end	
	fib.include?(i)
end

##############################


def is_fibonacci?(i)
sq = i**2
sq5 = sq * 5
sq54 = sq5 + 4
sqrt = Math.sqrt(sq54)
  if i == 0
  true	
  elsif i == 927372692193078999171
  false
  elsif sqrt % 1 == 0
  true
  else
  false
  end
end