Dear Uncle Colin,
I’m struggling to make any headway with this: find all integers $n$ such that $5 \times 2^n + 1$ is square. Any ideas?
Lousy Expression Being Equalto Square Gives Undue Exasperation
Hi, LEBESGUE, and thanks for your message!
Every mathematician should have a Bag Of Tricks – things they look out for that occasionally make problem-solving easier. Think of it as a mathematical toolkit. For me, it’s things like Clever Regrouping, Fermat’s Little Theorem, modulo arithmetic and – more often than the others – the difference of two squares.
It’s not immediately obvious…
Continue reading at: