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U N S O L V E D :

# Does any number appear exactly 5 times in Pascal's triangle?

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# Is there a square with integer side lengths and a point in the plane whose distance to each corner of the square is an integer?

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~~Find a method to determine whether or not any given knot is invertible~~.

# What is the best way to cut a donut up into tetrahedra?

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# Can you cut a rectangle into *3* congruent non-rectangular pieces?

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# Pick a positive whole number *n*; if odd, replace with *3n+1*, if even divide by *2*, repeat ...

# Are there infinitely many even perfect numbers?

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# Every even number greater than 2 is the sum of 2 primes. True or false?

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