Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

We are given our bounds in the problem, `1..4000000`

, and we are to find and sum every even fibonacci number inside the given bounds.

To start off, we should define a function to generate a list of fibonacci numbers. I opted for a recursive function, but this could easily be achieved using simple loops as well.

def fib(nums, maxNum):
if not (nums[-1] >= maxNum):
nums.append(nums[-1] + nums[-2])
fib(nums, maxNum)
return nums

With that function defined, the rest of the problem is simply iterating through the array of fibonacci numbers, testing if they are even, and adding them to a sum value.

Python Implementation

def main():
nums = [1,2,3]
maxNum = 4000000
nums = fib(nums, maxNum)
fibSum = 0
for num in nums:
if (num % 2) == 0:
fibSum += num
print(fibSum)
def fib(nums, maxNum):
if not (nums[-1] >= maxNum):
nums.append(nums[-1] + nums[-2])
fib(nums, maxNum)
return nums
if __name__ == "__main__": main()