Showerthoughts

29786 readers

255 users here now

A "Showerthought" is a simple term used to describe the thoughts that pop into your head while you're doing everyday things like taking a shower, driving, or just daydreaming. A showerthought should offer a unique perspective on an ordinary part of life.

Rules

All posts must be showerthoughts
The entire showerthought must be in the title
Avoid politics
- 3.1) NEW RULE as of 5 Nov 2024, trying it out
- 3.2) Political posts often end up being circle jerks (not offering unique perspective) or enflaming (too much work for mods).
- 3.3) Try c/politicaldiscussion, volunteer as a mod here, or start your own community.
Posts must be original/unique
Adhere to Lemmy's Code of Conduct

founded 1 year ago

MODERATORS

[email protected]

253

Amazon should've made Prime Day fall on a date corresponding to an actual three-digit prime number. (sh.itjust.works)

submitted 4 months ago* (last edited 4 months ago) by [email protected] to c/[email protected]

43 comments fedilink hide all child comments

Amazon is running a Prime Day sale on July 16 and 17. Setting aside the fact that this is two separate days, neither 716 nor 717 are prime numbers. They should've done 7/19 instead.

you are viewing a single comment's thread
view the rest of the comments

[–] [email protected] 4 points 4 months ago

It works differently for each number. For 2, the last number has to be divisible by 2. For 3, the sum of the digits has to be divisible by 3 For 5, the number has to end with a 0 or a 5. For 7, it is kinda tricky. Take the last digit, double it, and subtract it from the numbers on the left. If the remainder is 0 or divisible by 7, the whole number is divisible by 7. For example 49: 9×2=18, 4-18=-14, -14/7=2 with remainder 0. For 700, 0×2=0, 70-0=70, 70/7=10 remainder 0.

This is usually specified for prime numbers, for non-prime number, you just do calculate the prime components of a number and combine the rules.

For example, divisibility by 15: it has to be divisible by 3 and 5. 1+5=6, 6/3=2 remainder 0. 15 ends with a 5. For number where with multiple same prime components the rules for these duplicate numbers have to apply multiple times. Like for 25, it has to end with a 5 or 0, and when dividing the number by 5, the result has to end with a 5 or a 0 aswell.