Meet Eratosthenes, the Father of Geography, Librarian of Alexandria, and 3rd century BCE polymath. Click the green flag and he'll introduce himself, then use his famous sieve to tell you if the number you type is prime or composite. (1 is neither prime nor composite, so don't try that or you'll get such a scolding!)
Today's prompt gave me all sorts of fits. I could not think of a block that I WANTED to know more about. I know that there are blocks that I do not know how to use, (I'm looking in your direction, "abs/cos/sin/etc. of...") but I didn't really want to know more about them. That is most likely because I do not know how one might use them. Then I thought, like Eliza Bennet and the pianoforte, if I don't know how to use those blocks, I should suppose that to be my own fault because I have not taken the trouble to practice with them. So I knew that I would have to choose something from the operators palette. (I had a decades long feud with math that began with some bad encounters in elementary school. When I started teaching, the process of reconciliation began, and continues to this day.) After angsting over the various operators, and casting about for something I might be able to use them for that would stretch my thinking and programming, I happened to notice a book on the shelf called "The Librarian Who Measured the Earth". It's a picture book biography about Eratosthenes of Cyrene. I read it to my 5th graders back in the day when we started studying prime and composite numbers. So I decided to try to write a program that would, like the Sieve of Eratosthenes, determine if a given number is prime or composite. So I decided that I would use "...mod..." and create functions (which I have seldom used) to determine if an input number is evenly divisible by 2, 3, 5, or 7. While I have tinkered with these blocks before, I do not think I have ever used them in a finished project. I also ended up using "broadcast... and wait" which I think I have used before, but certainly not very often. The first thing was to get the math working correctly. My first challenge was handling the numbers from 2 to 7 because you don't need to run all of the divisibility tests on those. I ended up creating a script of nested "if... then, else..." statements to deal with those. If the number is greater than 7, a second script of nested if... else blocks runs and determines is the given number is prime or not. There was a lot of trial and error with this, but it was good exercise. When I taught 5th grade, the standard was that they had to be able to determine prime and composite numbers up to 100, so I set that as the ceiling on this project. (The code actually works up to 120, but it was tedious enough creating a sprite with a costume for all of the numbers 2-100.) I put in a check that the user's entered number is from 2 to 100. If they enter an invalid number, they get reminded to enter a number in the correct range. I know there is a more elegant way to accomplish what I did, and I was tempted to go looking for it. However, stubbornness won the day and I puzzled out my own bulky, but effective way. After the math was under control I added the text to speech blocks with the instructions and the biographical information. Then I coded the basket sprite to wiggle side to side as a sieve and the number sprite to appear, drop into the sieve, and emerge as the word "prime" or "comp". (Composite is too long to hide behind my sieve sprite.) So what did I learn? I suppose it is that I need to take the time to practice with those operators. I don't know how to use them, so I do not know what I might be able to make if I did.
