Can you use repeating numbers like $\pi$, and $e$, as the Key to OTP ciphers? Since $\pi$ and other numbers repeat could you use them as a OPT key. Ex: a 5 character message is sent and the first 5 digits of $\pi$ are used. after that the next $X$ number of digits are used and so on. from what I understand of Cryptography (its my hyper fixation for the week) and potential 3rd party readers would have to know the number of messages sent and their length to try and decode the messages. if i understand it, it would be near impossible to brute force and would require digital forensics (data remanence can be an issue).
Obviously the community knows more than me, any insight would be much appreciated.
An OTP is completely broken if you use a key that can be predicted. As such, $\pi$ would be a terrible choice. The key needs to be unpredictable, nonrepeating, and completely random. $\pi$ satisfies the nonrepeating aspect, and (looks like it) satisfies the randomness attribute, but is predictable since I can simply search online for 1 million digits of $\pi$.
To clarify, any number people have actually heard of is a bad choice. $\pi$, $e$, the coefficient of rolling friction across a carpet, are all bad choices. You need to use a number that has never occurred before, and never will; aka randomly generated by you, not taken from a mathematical constant.