Is there a cheap or free software-based calculator that is capable of doing basic arithmetic with numbers that have millions of digits? It would be even better if you could input and output numbers in scientific notation. Also I'm not really experienced with coding, not sure if that will be relevant.
KBH Thousand Digit Op will multiply one-thousand digit numbers and will divide two-thousand digit numbers.
Otherwise, there are numerical libraries for the Unix and Linux C compiler. And the Unix and Linux C compiler has been ported to Windows. Also, there are numerical libraries for Python.
Julia can handle arbitrary numbers and is available for many platforms.
julia> # multiply a big number by two in julia:
julia> 1.9560*10^big(1834097) * 2