--- In

primenumbers@yahoogroups.com, "G Fischer" <golfbum71@...> wrote:

>

> Hit send again and realized I misspoke below for the 6N+1 multiplied by 6N-1

> numbers...

> c = 6ab + a - b

> This formula will show differently since a and b can be different... when

> the numbers are interchanged.

>

> As an example: 59*67 = 3953

> The formula for c in this case is: c = 6ab + a - b

> a = 10

> b = 11

> c = 659

> c = 6*10*11 - 10 + 11

> c = 660 + 1

> c = 661

>

> and flopped:

> a = 11, b = 10, c = 659

> c = 6*10*11 - 11 + 10

> c = 660 - 1

> c = 659

>

> Perhaps a rule for whichever number is 6N-1 is added and 6N+1 is subtracted?

It's not complicated at all, Geoff, it's just high-school algebra.

Let the 2 numbers be x=6*a+a1 and y=6*b+b1, where a1 and b1 are each either +1 or -1.

Then x*y = (6*a+a1)*(6*b+b1) = 6*c+c1,

where c = 6*a*b+a1+b1,

and c1 = a1*b1 (= +1 or -1).

Mike