Hi Anonymous Monk,

I will go with 50 :-)

1    =    1        # first pattern: p0
5    =    1 x  5   # p0 x 5
10   =    1 x 10   # p0 x 10
25   =    5 x  5   # p1 x 5
50   =    5 x 10   # p1 x 10
50   =   10 x  5   # p2 x 5
100  =   10 x 10   # p2 x 10
[download]

However, I also like the answer given by sulfericacid in Re: A script to determine the next number in a sequence. But as Limbic~Region said in Re: A script to determine the next number in a sequence: “For a given number of integers in a sequence, there are an infinite number of "formulas" that could produce that sequence.” This is why for your small dataset more than one answer is possible.

Cheers

lin0

Update: Added quote by Limbic~Region in attention to his comment in Re^2: A script to determine the next number in a sequence