The way the article uses RSA is no better than a simple substitution cipher. Both the "l"s in "hello" are enciphered to 2575. It's a newspaper cryptogram.

You're supposed to concatenate all the input numbers, to create a message that has hundreds or thousands of digits; then RSA-encrypt that number.

I have a different take on the same topic: https://www.nayuki.io/page/java-biginteger-was-made-for-rsa-...

My article isn't written as a step-by-step tutorial and doesn't come with example numbers. But mine fills in certain things that xnacly doesn't cover: random prime generation, efficiently calculating the decryption exponent d from (n, e) by using a modular inverse, using modular exponentiation instead of power-then-modulo.

By the way for Python, modular exponentiation is pow(x, y, m) (since 3.0), and modular inverse is pow(x, -1, m) (since 3.8, Oct 2019). https://docs.python.org/3/library/functions.html#pow

One of the bigger hurdles in implementing RSA is having an algorithm which can multiply the large numbers in real time. If you try a niave multiplication algorithm, you might find you'll never get an answer. A lot of hardware now comes with special instructions which implement efficient algorithms for doing this.

RSA is one of those algorithms where understanding it once actually sticks.