256
Amazon should've made Prime Day fall on a date corresponding to an actual three-digit prime number.
(self.showerthoughts)
this post was submitted on 17 Jul 2024
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How the hell is 717 not a prime number? Who fucked that up? I vote we just change that
Divisible by 3. Easy to check since 7 + 1 + 7 = 15 which is divisible by 3.
Oh awesome that's a neat trick I've never seen before. How does that work? For a number like 700 for example, 7 + 0 + 0 = 7 but 700 is visible by 10.
Back in the olden days before digital calculators, people had tricks like that to help them do mental math.
😂 I'm familiar with many of them because I liked math in school and went through all of primary and middle school without a digital calculator. This one is one I hadn't heard of before and, again because I like math, I'm interested in understanding 1) what the trick is and 2) mathematically how it works out