## 25157Re: Multiplying Primes and Numbers in General

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• Jun 4, 2013
--- In primenumbers@yahoogroups.com, "golfbum71" <golfbum71@...> wrote:
>
> I'm trying to find more resources to help verify something I've noticed. You guys are all math geniuses (okay most of you are...but I won't say who...) and I'm hoping someone can point me in the right direction.
>
> When multiplying two prime numbers...that can be expressed (we'll assume two 6N-1 numbers...) as (6a-1)(6b-1) = 6c-1. I've recently noticed that in this case, c can be expressed as: 6ab - b + a. (when there is one 6N+1 number, c = 6ab + a - b, and when there are two 6N+1 numbers, c = 6ab + a + b)
>
> I'm guessing this thought isn't original and probably several thousand years old...I just don't know where to look.
>
> By the way. this expression can be taken further for the multiplication of any two numbers if expressed from 6N-2 to 6N+3.

Hi Geoff,

I'm afraid there are so many errors in your algebra that it's hard to know where to start...

It's always a good idea to double-check before posting, by putting in at least one set of values.
Let's take the primes 5 and 11, so a=1, b=2.
The product is 55.
Is this of the form 6c-1, with c=6ab - b + a?
I don't think so !

Anyway, a formula of that kind can't be right, as interchanging a and b gives a different answer, but multiplication is commutative.

Another general point: I should have thought that whether or not the numbers are /prime/ must be irrelevant in equations of the kind you are considering, no?
Try some non-prime numbers.

Best regards - and better luck next time !

Mike
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