The above integral is equal to where are all positive integers.
Find
Note : denotes the fractional part and denotes the Euler-Mascheroni constant.
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First note that ∫ 0 1 { x 1 } { 2 x } x d x = ∫ 0 2 1 { x 1 } 2 x x d x + ∫ 2 1 1 { x 1 } ( 2 x − 1 ) x d x = 2 ∫ 0 1 { x 1 } d x − ∫ 2 1 1 { x 1 } x d x and ∫ N + 1 1 1 { x 1 } d x = n = 1 ∑ N ∫ n + 1 1 n 1 { x 1 } d x = n = 1 ∑ N ∫ n + 1 1 n 1 ( x 1 − n ) d x = ∫ N + 1 1 1 x d x − n = 1 ∑ N n ( n 1 − n + 1 1 ) = ln ( N + 1 ) − H N + 1 + 1 for any N ∈ N . Letting N → ∞ gives ∫ 0 1 { x 1 } x d x = 1 − γ Since ∫ 2 1 1 { x 1 } x d x = ∫ 2 1 1 ( x 1 − 1 ) x d x = 1 − ln 2 we deduce that ∫ 0 1 { x 1 } { 2 x } x d x = 2 ( 1 − γ ) − ( 1 − ln 2 ) = 1 + ln 2 − 2 γ making the answer 1 + 2 + 2 = 5 .