Thanks for the welcome messages! I have written a few posts on the UCF and the recently closed DCF in the last few years, and I saw some of DJ's old posts on the UCF. And before the CasioScene drama happened I was a registered user at CasioKingdom. The restore to an old backup over there removed all evidence of that, but I won't go back there because it's become a toyland for spambots.
The permissions seem a bit screwed up, because I tried the test message you suggested, and it actually worked. I understand why this limit is in place (look at CasioKingdom to see what happens without such protection), and I think someone should enforce what that post in the news section says. I can only assume this no-PM rule has been softened, because I had to solve a captcha like at my registration. (Not a problem for a human, though.)
So with the PM way apparently working, I'll use it.

Thanks for the welcome messages! I have written a few posts on the UCF and the recently closed DCF in the last few years, and I saw some of DJ's old posts on the UCF. And before the CasioScene drama happened I was a registered user at CasioKingdom. The restore to an old backup over there removed all evidence of that, but I won't go back there because it's become a toyland for spambots.
The permissions seem a bit screwed up, because I tried the test message you suggested, and it actually worked. I understand why this limit is in place (look at CasioKingdom to see what happens without such protection), and I think someone should enforce what that post in the news section says. I can only assume this no-PM rule has been softened, because I had to solve a captcha like at my registration. (Not a problem for a human, though.)
So with the PM way apparently working, I'll use it.

Yeah I wish that CK forums owners added more anti-spams on the site after the restoral. It was old but it had lots of useful info. I guess for Omni the permissions were messed up in the upgrade we also had a few months ago. Admins will probably re-instate the post limit if more bots come in here, but let's hope the bots won't do so.

Also I didn't know that DCF closed, that sucks

Here's my suggestion for the next challenge:

Input: a positive integer of reasonable size
Output: The highest prime factor of that integer, in binary, but with all 0s replaced with underscores (_) and all 1s replaced with minus signs (-)

Example:
Input: 15
Output: -_-

Example:
Input: 7
Output: ---

Example:
Input: 115
Output: -_---

Here's my suggestion for the next challenge:

Input: a positive integer of reasonable size
Output: The highest prime factor of that integer, in binary, but with all 0s replaced with underscores (_) and all 1s replaced with minus signs (-)

Example:
Input: 15
Output: -_-

Example:
Input: 7
Output: ---

Example:
Input: 115
Output: -_---

This is the kind of creatively new yet simple challenge that I wish I could think of.

I don't think there are underscores in TI BASIC, but I'll try if you win

There is an underscore token, although it's not typeable on a calculator through normal means. It's two-byte code is BBD9. It could be entered either in a computer tokenizer or perhaps produced by an on-calc tool made for producing untypeable characters, like this.

Looking over the solutions, I noticed that the shortest Java version does not process one string, but instead assumes someone has split it already and put the parts into the command-line parameters array before the program starts. On the other hand, it shows how my solution could be shortened further (println ->print, and I could have omitted curly braces around the body of the for loop).
Edit: And that version apparently has a bug, it prints the entire array when it failed to parse one element to an integer. There are three characters missing (a+' ' should be a+' '). Due to the size being 171 instead of 174, they apparently got lost somewhere between size measurement and code posting.

I assume there are some languages with an advantage for the new challenge above. If you have a CAS-equipped calculator, the factorization is as simple as a function call, on most other languages you'll have to implement it yourself. Though such a discrimination is hard to avoid.
Luckily the 50G has a CAS, so I already have a 57-byte SysRPL solution. The other languages I used will be a bit harder.

Okay, challenge accepted, I'm going to cut that one down.
String[] aDrop the space, 1 byte saved.
for(String t:a){...}Drop the curly braces, 2 more bytes down (I just saw that in my submission as well). Your other solution already has that.
s+=i;System.out.println(s);Two things here: Drop the ln (like in your submission), 2 bytes saved. The concatenation of string and number can be done inside the parentheses of the print, saving 3 more bytes.
Total improvement: 8 bytes, so the size is 161 now.

Welp, I just learned I could cut out 4 bytes in my Ruby entry by shortening "print" with "p" o.o

Welp, now I know.