I am getting married and quite a few of my guests are mathematicians. I would like to design an invite with a puzzle. Basically, I would like to pose a short puzzle with the answer 26.
My example (but might be too easy (it can be solved with the knowledge of quadratic equation)).
$$ a+b = 4 $$ and $$ a^2 + b^2 = 10 $$ then $$ a^3 + b^3 -2 = ? $$
However, it need not be a number theory question. Thank you for your time.