Lychrel Numbers

This could get tricky if we were working with fixed size integers, since the reverse-and-add process for Lychrel numbers can result in some big numbers. But Python ints have unlimited precision, so no need to worry about that.

def is_palindrome(n):
    s = str(n)
    return s == s[::-1]


def is_lychrel_number(n):
    for _ in range(0, 50):
        rev = int(str(n)[::-1])
        n += rev
        if is_palindrome(n):
            return False
        
    return True

This is easy to brute force, since we're not checking that many numbers, and we loop at most 50 times in our test.

lychrel_numbers = {n for n in range(1, 10000) if is_lychrel_number(n)}

len(lychrel_numbers)

249

Relevant sequences

• Suspected Lychrel numbers: A023108

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