Op, I already solved this. Here is the thread:

Thread: The Amazing Prime Number Matrix

All you have to do is write out the numbers back and forth like this:

xx xx xx x0 x1 x2 x3
x9 x8 x7 x6 x5 x4 xx
xx 10 11 12 13 14 15
21 20 19 18 17 16...and so on...

All the primes will be in two columns (the 7 and 5 columns) with multiples of 6 always being in the 6 (i.e. middle) column.

The only exception is that multiples of all the primes will also appear in the 7 and 5 columns as well, you just have to remove those as you go.

You can find them by drawing a frequency wave along the matrix for each prime number. Wherever it intersects on the 7 or 5 column, that number is not prime. All the rest are therefore prime by default. See the other thread for details.