Even Fibonacci Numbers¶

There's a lot to learn about the Fibonacci numbers, and this will not be the last time we see them in a Project Euler problem, but for now this problem keeps it relatively simple.

Since this is a SageMath notebook, we'll use its functionality so we can keep our code simple like the problem.

In [1]:
sum(n for n in fibonacci_xrange(1, 4000000) if n % 2 == 0)
Out[1]:
4613732

Even without SageMath, it's easy to implement our own generator of the sequence up to $n$.

In [2]:
def fib(n):
    a = 0
    b = 1
    while a <= n:
        yield a
        a, b = b, a + b

Relevant sequences¶

  • Fibonacci numbers: A000045
  • Partial sums of even Fibonacci numbers: A099919

Copyright (C) 2025 filifa¶

This work is licensed under the Creative Commons Attribution-ShareAlike 4.0 International license and the BSD Zero Clause license.