Here is a "theorem" I learned: every number up to 100 which looks prime, is prime, except 91. Does anyone recall its name?
I think it's called "The Ridiculous Fish Theorem."
+1... I lost two games in a row, both times on 91.
Is This Prime?
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Re: Is This Prime?
#22Great game!
Keyboard short cuts would make it a bit better.
Re: Is This Prime?
#23This reminds me of my favorite in-person magic trick to do. First, memorize all the two-digit primes. 25 numbers isn't that hard to memorize. Then, tell someone "Oh, I can instantly tell whether a number is prime or not. Give me a number, I'll tell you whether it's prime." If they tell you a number between 1 and 100, use your memorized list. Otherwise, it's a game of cold reading; if they just generated a random stri…
And then one day, somebody asks you calmly: "what about 2^31-1"? Better memorise the small Mersenne exponents as well!
Re: Is This Prime?
#24Re: Is This Prime?
#25They've included 1 as not a prime. That was a fairly recent decision.
One is not a prime number. If you allow one to be a prime number, then you can no longer say that each natural number has a unique prime factorization.
This makes the concept of prime numbers much more useful when one is excluded.
Re: Is This Prime?
#26Here is a "theorem" I learned: every number up to 100 which looks prime, is prime, except 91. Does anyone recall its name?
This is a great "theorem", thank you!
It's easy to determine divisibility by 2, 3, 5, and 11. 7² is also easy because it's a square. 7×13=91 is the only composite number under 100 that isn't caught by these rules.
Re: Is This Prime?
#27Why do I feel like I'm solving someone else's CAPTCHA?
Re: Is This Prime?
#28Finally a way to sort out candidates that's even cheaper than making them implement B-trees.
Re: Is This Prime?
#29I'm not sure why but having 'yes' be on the left is really messing me up.
You must be a macOS or iOS user.
Re: Is This Prime?
#30Here is a "theorem" I learned: every number up to 100 which looks prime, is prime, except 91. Does anyone recall its name?
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