In case you're wondering about the title, this is kind of a little challenge: try to find the shortest RPN keystroke sequence that makes the 42S display **42.4242424242**, assuming the display mode is STD or at least FIX 10. Simply keying the number in would require 13 keystrokes, so only solutions up to 12 keystrokes would count. I have found a 7-keystroke sequence which has the additional advantage to be almost universal: if your calculator of choice is the HP-41 you'd be able to use the same number of keystrokes to display **41.41414141** on it. And so to display **15.15151515** on your 15C, and **12.12121212** on your 12C, and so on.

A variation would be considering the calculator in its initial power-on state. In the case of the HP-41 it defaults to FIX 4. So we'd like to display **41.4141** instead as **shift FIX 9** would require three more keystrokes, which would spoil the fun. Of course displaying **41.4141** would require at least 8 keystrokes (ENTER is needed to hide the cursor). Interesting solutions should have 7 keystrokes at most. For instance, the 5-keystroke sequence **2 SQRT 40 +**would be a nice solution if it returned 41.4141 rather than 41.4142.

I came across the more general solution in less than ten minutes, which makes me guess this is a very easy challenge after all (or I was just lucky). The other solutions might be more interesting in case you're willing to try (so far I don't have any).

Best regards,

Gerson.