How to find the a certain index of a string [Python]

I am creating a program that is a hybrid of the Vigenere Cipher and the RSA Algorithm. For the code, I need to find certain indexes of a string. E.G. encrypted = '10134585588147, 3847183463814, 18517461398', where there are 3 indexes each separated by commas. Now I want to get the second index, how would I do this. This is just an example and I need to be able to get certain indexes without knowing how long the encrypted string is.

Thanks for helping.