How many ways are there of filling an $$n\times n$$square grid with 0s and 1s if you are allowed at most two 1s in each row and two 1s in each column?

Question

anonymous · Answer

Where do you come up with this stuff?

anonymous · Answer

...a textbook

anonymous · Answer

The same textbook that wanted the dragon curve and Mandelbrot set?

anonymous · Answer

yes

anonymous · Answer

it's a really good book though

anonymous · Answer

What's the name/author?

anonymous · Answer

http://www.amazon.com/Princeton-Companion-Mathematics-Timothy-Gowers/dp/0691118809/ref=cm_cr_pr_product_top

anonymous · Answer

Good problem.

anonymous · Answer

Sounds good.  I'll try to check it out.

anonymous · Answer

it's like the bible of mathematics, the modern "The Principles of Mathematics"

anonymous · Answer

I must return it to the library tho :-(

anonymous · Answer

That first amazon review said there are parts of it online.

anonymous · Answer

I got numbers for the first four n's:
2: 16
3: 265
4: 7343
5: 304,186
My program is O(2^(n^2)) so 6 will take a good long time (probably a week).