Calculate the Collatz Conjecture in APL :)

The Collatz conjecture is one of the most famous unsolved problems in mathematics. The conjecture asks whether repeating two simple arithmetic operations will eventually transform every positive integer into 1. I wonder how big of a number the echo show will calculate? Is it an unsigned 64 bit integer (long), or is it a 32 bit integer (int)?

This is the biggest number: 1000000000000000000. Nice!