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Let us denote Sn = an + bn + cn for arbitrary numbers a, b, c. It is known that S1 = 8, 5, S2 = 74, 25, S3 = 639, 625 for some values of a, b, c. What is the largest possible value of S2811 — S810S812


Kate drew a 41 x 41 checkered square (lattice) on the asphalt with white chalk (i.e. there are 42 horizontal segments and 42 vertical segments drawn).

By one move it is allowed to pick out an arbitrary square (of any size) and repaint its boundary using a chalk of blue colour. In different moves it is allowed to repaint any segment more than once. What is the smallest number of such moves required to repaint all the initial lines in blue colour?


Let us denote Sn = (a^n) + (b^n) +( c^n) for arbitrary numbers a, b, c. It is known that S1 = 8,5, S2 = 74, 25, S3 = 639, 625 for some values of a, b, c. What is the largest possible value of (S811)^2 - S810.S812?

36 students are members of a sports club. Every two of them are either friends or enemies. (Friendship and enmity are reciprocal, i.e. if A is a friend to B then B is a friend to A, and the same applies to being enemies.) It has turned out that each of the students has exactly 8 enemies. Let us call a group of three students concurrent if they are either pairwise enemies or pairwise friends to each other. What is the maximum possible quantity of concurrent student triples in this sports club? (Two distinct concurrent student triples may have mutual students in them.)


Consider the following sequence of successive numbers of the 2k-th power:

1, 2^2k, 3^2k, 4^2k, 5^2k, ...

Show that the difference between the numbers in this sequence is odd for all k ∈ N.

Find a counter example to the statement that every even positive integer can be written as the sum of the squares of three integers.


A local restaurant is offering a free meal to every 25th customer and a free hat to every 12th

customer. Which customer will be the first to get both a free meal and a free hat?
120 numbers are written on the board. It is known that among all their pairwise

products there are exactly 2000 negative numbers. What is the largest number of

zeroes that could be written on the board?
Statement: “The product of an even number and any other number is even.”

Using direct proof method.
Statement: “The negative of any even integer is even.”

Using direct proof method
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