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Squared average equals square (Posted on 2019-08-09) Difficulty: 3 of 5
Find n consecutive perfect squares (n > 1)whose average is n2.

No Solution Yet Submitted by Danish Ahmed Khan    
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re: computer solution | Comment 2 of 3 |
(In reply to computer solution by Charlie)

n=47, x=-68 is a solution, as negative integers also have perfect squares.


Let sum n=1 to n (x+n)^2 = n^3

Then 1/6n(2n^2+n(6x+3)+6x^2+6x+1) = n^3, so

1/6(2n^2+n(6x+3)+6x^2+6x+1) = n^2, or
1/12 (n^2 - 1) + 1/4 (n + 2 x + 1)^2 = n^2

{{n == 1, x == -2}, {n == 1, x == 0}, {n == 47, x == -69}, {n == 47, x == 21}, {n == 2161, x == -3150}, {n == 2161, x == 988}} etc. 

A189173 gives the value of n but does not specify the consecutive squares.

Edited on August 9, 2019, 11:08 pm
  Posted by broll on 2019-08-09 22:59:25

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