#2: Even Fibonacci numbers | Ben Cunningham

#2: Even Fibonacci numbers

Problem by Project Euler · on October 19, 2001

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:

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

Python

ans = 2
terms = [1, 2, 3]
max = 4000000

while terms[2] <= max:

    terms[0:2] = terms[1:3]
    terms[2] = sum(terms[0:2])

    if (terms[2] % 2 == 0) and (terms[2] <= max):
        ans += terms[2]

print(ans)
## 4613732

R

x <- 1:2
max <- 4000000

while (tail(x, 1) < max) {
  x <- c(x, sum(tail(x, 2)))
}

sum(x[x %% 2 == 0 & x <= max])
## [1] 4613732