Even Fibonacci Terms

Computer Science Level pending

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


The answer is 4613732.

Shaksham Kapoor by Shaksham Kapoor , 26, India

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1 solution

Bill Bell
Oct 28, 2014

Alternative 1: 

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def fib ( ) :
    t0, t1 = 1, 2
    yield t0
    yield t1
    while True :
        t2 = t0 + t1
        t0, t1 = t1, t2
        yield t2

f = fib ( ) 
sum = 0
while True :
    term = f . next ( )
    if term <= 4000000 :
        if term % 2 == 0 :
            sum += term
    else :
        break
print sum

Alternative 2:

Get the terms from http://oeis.org/A000045. Copy and paste them into a list. Make the calculation using a list comprehension. 

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fs=[    0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 28657, 46368, 75025, 121393, 196418, 317811, 514229, 832040, 1346269, 2178309, 3524578, 5702887, 9227465, 14930352, 24157817, 39088169]
sum([i for i in fs if i % 2==0 and i <=4000000])

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