# Prime Directive ?

By pgn

@pgntwo (21990)

Derry, Northern Ireland

May 17, 2017 3:06pm CST

Here's one for the mathematicians amongst us.
Most people know that a prime number is only divisible by itself or by 1, for example, the number "31".
So if you keep placing a 3 in front of 31, (331; 3,331; 33,331...), it stays prime until it reaches 333,333,331 (which factors into 19,607,843 x 17).
Why is that, I wonder...?
PS. I tested out some of the possibilities on WolframAlpha, a mathematical search engine, adding or removing a 3 each time:

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16 people like this

16 responses

@arthurchappell (33979)

• Preston, England

18 May 17

@pgntwo maths usually causes my mind to disintegrate

4 people like this

@pgntwo (21990)

• Derry, Northern Ireland

18 May 17

Ah, a numerohobe, or an arithmophobe?

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3 people like this

@DesirousDreamer (23940)

• Peoria, Arizona

17 May 17

I feel like someone has to be very bored to figure that out haha! But interesting nonetheless!

3 people like this

@Poppylicious (9520)

•

18 May 17

I'm afraid that I completely switched off when you mentioned the word mathematician. *makes the sign of the cross*

3 people like this

@Susan2015 (21336)

• United States

20 May 17

Math was my absolute worst subject in school.

2 people like this

@DaddyEvil (25818)

• Aurora, Missouri

20 May 17

Hmmm... I am nowhere close to a mathematician, pgn... (I'm lucky I know what a prime number is, let alone most things involving math!)
Yes, I can add, subtract, multiply and divide in my head quite quickly, but you really should talk with @sishy7 about things like this! LOL!

1 person likes this

@DaddyEvil (25818)

• Aurora, Missouri

21 May 17

@pgntwo Hmmm... not sure about that, pgn... maybe just the greedy people who hire them!

2 people like this

@pgntwo (21990)

• Derry, Northern Ireland

21 May 17

@DaddyEvil It could be - but the controllers must be hot with numbers too, I'd guess.

1 person likes this

@much2say (40077)

• United States

17 May 17

My daughter has recently had to deal with good 'ol prime numbers and factoring in her math class . . . math makes her head hurt as much as it does mine (especially the way they teach it these days ). I wonder if her teacher knows about this one .

1 person likes this

@Mike197602 (13899)

• United Kingdom

17 May 17

I got a few A's in GCSE's and A levels...maths was not among the A's
PS...this discussion reminded me of Optimus Prime from the transformers...when pissed I look at his end speech from the film on youtube

1 person likes this

@Mike197602 (13899)

• United Kingdom

17 May 17

@pgntwo I like the linkin park track and I'm a fan of the megan fox/shia lebouf, or whatever his name is, films.

3 people like this

@pgntwo (21990)

• Derry, Northern Ireland

18 May 17

I had a play with this number series on the mathematical search engine, WolframAlpha, here's a sample - add or remove 3s until it starts to be "not prime":

1 person likes this