This section is about official bonus problems of Project Euler.
These sometimes pop up after you solve another problem, and it is not well documented when they show up.
According to their copyright statement, these problems are copyrighted unlike the others, so we can't reproduce them here. But we can give answers I believe.
This was a registration CAPTCHA problem as of 2025:
Among the first 510 thousand square numbers, what is the sum of all the odd squares?
Bash + Python "one-liner":
python -c $'import sys;max=int(sys.argv[1]) + 1;s = 0\nfor i in range(1, max, 2):\n s += i*i\nprint(s)' 510000
With indentation:
s = 0
for i in range(1, 510001, 2):
    s += i*i
print(s)
As a file at: euler/0.py
Popped up for Ciro Santilli on April 19th 2026 after solving Project Euler problem 993.
The problem is available only as an image. Furthermore, the problem image itself, i.e.:
wget -O secret.png https://projecteuler.net/resources/images/bonus_secret_statement.png?1738588439
(I hope it's not fingerprinted to my login lol) must be passed as an input of your solver.
The output of the program is another image of Euler with caption:
THE SECRET WORD IS MY FIRST NAME
so and the final answer must be inferred to be the string:
Leonhard
ChatGPT web 5.4 solved it directly from the image.

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