What does $5p² + p \mod 26$ mean?

Question

I need to encrypt a message using 5p² + p mod 26 but i'm not sure what 5p² + p means? I understand how to do it but I just need to know what it's meant to stand for.

Thank you for any help

Answer 1

Most likely you are supposed to number the letters you have from $0$ to $25$, and then use the formula to encode every letter, for example, like so:

If your plain text letter is $E$, then $E = 4$, in the standard alphabetical order, starting at $0$, so the crypto letter becomes:

$$5*4^2 + 4 = 5*16 + 4 = 84 = 3*26 + 6 = G$$

Answer 2

That is the remainder of $ 5p^2+p$ when divided by $26.$ For example if $p=7$ then $5(7^2)+7=250$ and the remainder of $250$ in dividing by $26$ is $16.$