Project Euler problems solved with Python

Background:

Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. Although mathematics will help you arrive at elegant and efficient methods, the use of a computer and programming skills will be required to solve most problems.

In this post, I am going to solve the first five problems. I will code the solutions for the remaining problems as time permits. My solutions are also on Github.

Problem one:

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

Solution:

print(sum([x for x in range(1000) if (x % 3 == 0) or (x % 5 == 0)]))

Problem two:

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.

Solution:

def fibonacci_gen(n):
    a, b = 1, 1
    while b <= n:
        a, b = b, a + b
        yield a

def solution(n):
    return sum(i for i in fibonacci_gen(n) if not i % 2)

if __name__ == '__main__':
    print(solution(4000000))

Problem three:

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143?

Solution:

the_number = 600851475143
prime = 2

while prime * prime < the_number:
    while not the_number % prime:
        the_number //= prime
    prime += 1

print (the_number)

Problem four:

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.

Solution:

i = 100
p = []

while i <= 999:
    for j in range(i, 1000):
        number = i * j
        var = str(number)
        if var == var[::-1]:
            p.append(int(var))

    i += 1

print(max(p))

Problem five:

2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.

What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?

Solution:

i = 1
for j in (range(1, 21)):
    if i % j > 0:
        for k in range(1, 21):
            if (i * k) % j == 0:
                i *= k
                break
print(i)

I will add the remaining solutions to this post.