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smc

number theory intermediate

Problem

Let be the set of all numbers which are the sum of the squares of three consecutive integers. Then we can say that
(A)
(B)
(C)
(D)
Solution
Consider consecutive integers and . Exactly one of these integers must be divisible by 3; WLOG, suppose is divisible by 3. Then and . Squaring, we have that and , so . Therefore, no member of is divisible by 3. Now consider more consecutive integers and , which we will consider mod 11. We will assign such that and . Some experimentation shows that when so . Similarly, so , and so . Therefore, , so there is at least one member of which is divisible by 11. Thus, is correct.
Final answer
B