100000000 (10^8) digits automorphic number
The large number X in result (base-10 with reversed order i.e. from lowest digit to highest digit)
is a automorphic number (https://en.wikipedia.org/wiki/Automorphic_number)
Check it with check.py (with enough memory like 16GB?). numpy is needed. If you want to use NTT,
sympy is needed (much slower than FFT)