Albert has pieces of paper numbered 1 to . He removes pieces of paper, numbered consecutively. The sum numbers on the remaining pieces of paper is equal to 1615. Find the sum of all possible values of .
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Total sum of all pages is 2 n ( 2 n + 1 ) / 2 = n ( 2 n + 1 )
Let the papers Albert took is starts with the positive integer k .Then consecutive n papers are k , k + 1 , k + 2 , . . . . . , k + n − 1 .Sum of these papers is n k + n ( n − 1 ) / 2 .
According to the question n ( 2 n + 1 ) − n k − n ( n − 1 ) / 2 = 1 6 1 5 .Re-arranging the equation
n ( 3 n + 3 − 2 k ) = 2 × 5 × 1 7 × 1 9
If n is odd then 3 n + 3 is even and 3 n + 3 − e v e n = 2 k so, 2 k will be even and k will be an integer. ..But we have to check k + n − 1 ≤ 2 n .And it is easy to check no odd value will be allowable.
If n is even 3 n + 3 is odd and 3 n + 3 − o d d = 2 k .Again k will be an integer.Here k satisfy the above condition that is k + n − 1 ≤ 2 n .So, n = 3 4 , 3 8 are only solutions.