Comment by genewitch

If you search sequentially, or start from the highest known failed number, you can also short circuit every even number you start on, as well as any number that goes below the start number. My code it requires copies of huge numbers, but I barely understand why the conjecture is special.

Anyhow I wrote a single-threaded collatz "benchmark" that does this using bigint and its hilarious to run it up around 127 bit numbers, inlet it run for 3 or 4 days and it never finished the first number it was given.

My github has a Java and Python version that should produce identical output. Collatz-gene or so.