Can the sum of 2023 consecutive perfect squares be equal to a perfect square?
• If so, provide an example.
• If not, prove that thre are no instances in conformity with the given conditions.
The sum of the first n squares is:
n(n+1)(2n+1) / 6
If you start with the k-th square and sum the next 2023 of them, the result is
(k+2023)(k+2024)(2k+4047) / 6 - k(k+1)(2k+1) / 6
((2k^3 + 12141k^2 + 24567313k + 16570651944) - (2k^3 + 3k^2 + k)) / 6
(12138k^2 + 24567312k + 16570651944)/6
(2023k^2 + 4094552k + 2761775324)
2023(k^2 + 2024k + 1365188)
2023(k^2 + 2024k + 1024144 + 341044)
2023((k + 1012)^2 + 341044)
Given 2023(k^2 + 2024k + 1365188), the quadratic must be divisible by 2023 for the expression to be a square.
The last term, 1365188, is 1686 mod 2023
The second term, 2024k mod 2023 is (k mod 2023)
So, (k^2 + k + 1686) must be 0 mod 2023
A brute force program shows that this last expression can take on 548 values, but zero is not one of them. Thus no value of k satisfies this condition.
The sum of 2023 consecutive squares is never a perfect square.
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Posted by Larry
on 2023-08-24 08:19:05 |