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IMO 1964 - Problem 6

Problem: Given a tetrahedron ABCD, let D1 be the centroid ò the triangle ABC and let A1,B1,C1 be the intersection points of the lines paral...

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    Problem: For any positive integer $k$, let $f(k)$ be the number of elements in the set $\left\{k+1,k+2,...,2k\right\}$ whose base $2$ repre...
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    Problem: Find all the three-digit numbers for which one obtains, when dividing the number by $11$, the sum of squares of the digits of the ...