It is also known as the 3n + 1 problem, the 3n + 1 conjecture, the Ulam conjecture.
# Build
git clone <this_repo>
cd <this_repo>
mkdir -p build/tmp
cd build/tmp
cmake ../..
make
# Run
cd ../bin/Release_Linux_x86_64/
./CollatzConjecture --input_num 123123
https://www.youtube.com/watch?v=094y1Z2wpJg&ab_channel=Veritasium (image from here)