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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