Here lies a library for Elm that allows you to operate on Integers (like the Haskell or Python ones). These Integers have no bounds other than the memory on your device, so you should be able to do millions of digits without difficulty.
Bear in mind the arithmetic is slower than with native Ints.
Add it to your elm-package.json. Import Data.Integer.
If something is broken, please create a bug report in Github: https://github.com/javcasas/elm-integer/issues
This library was made by Javier Casas. See full licence in the LICENSE file.