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Subject: Upper Bound:: number of pawn positions in chess...

Author: KarinsDad

Date: 07:32:30 01/13/00

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[D]2p5/1p1p4/p3p3/5p2/6p1/7p/8/8 w

As can be seen here, there are 30 possible pawn positions for a pawn on the c
file (i.e. all of the squares within this "triangle").

If I have done my math correctly:

a: 21
b: 26
c: 30
d: 32
e: 32
f: 30
g: 26
h: 21

So, an approximate of the number of white pawn positions is 21 * 26 * 30 * ...
or 274,743,705,600.

Therefore, the upper bound is this number squared (two colors) or 7.548e24.

Now, since these "triangles" of all possible pawn positions for a given pawn
overlap each other (i.e. two or more pawns could be in the same square), this
number is obviously too high.

The real calculation would be closer to 21 * 25 * 28 * 29 * ..., but even this
is too high.

In other words, for every a pawn placement, if it overlaps with a possible b
pawn placement, then the number of b pawn placements must be decreased by one,
etc.

If I had to guess, I would think that the real number would be in the ballpark
of about 1e20 or so.

Note: I disregarded a given pawn being off the board completely since that small
fraction would be gobbled up by the overlapping pawns. However, you could figure
out a different upper bound with 22 * 27 * 31 * ...

KarinsDad :)



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