[flagged]
https://www.jsoftware.com/ioj/iojATW.htm
Have you seen anything written in K itself? Here's a program to calculate primes:
2_&{&/x!/:2_!x}'!RI was not convinced of the readability of APL, but compared to its successors which tried to stick to ASCII, I've learned to appreciate the merits of an extended character set.