rpn 4.3.0
rpn 4.4.0
rpn 4.5.0
rpn 4.6.0
rpn 4.7.0
rpn 4.8.0
rpn 4.9.0.fast

Considering different alternatives for caching precomputed prime
numbers.
rpn 4.9.0.slow
rpn 4.9.0
rpn 4.10.0
rpn 4.11.0
rpn 4.12.0
rpn 4.13.0

mathworld.wolfram.com for the win!
rpn 4.14.0

The beginning of help!
rpn 4.15.0
rpn 4.16.0
rpn 4.16.1
rpn 4.17.0
rpn 4.17.1
rpn 4.18.0