The above integral has the following closed form: Here, are positive integers and all fractions are irreducible with prime then find .
Notation: denotes the Glaisher-Kinkelin constant .
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Consider: I ( a ) = ∫ 0 ∞ e 2 π x − 1 x a d x Rewrite it as: I ( a ) = ∫ 0 ∞ 1 − e − 2 π x x a e − 2 π x d x Using the Geometric Infinite Series and setting t = 2 π x : I ( a ) = ( 2 π ) a + 1 1 r = 1 ∑ ∞ r a + 1 1 ∫ 0 ∞ t a e − t d t which is by definitions of Zeta and Gamma Functions: I ( a ) = ( 2 π ) a + 1 Γ ( a + 1 ) ζ ( a + 1 ) Now, the required integral can be split up as: ln ( 2 π ) I ( 1 ) + I ′ ( 1 ) Using the fact that ζ ′ ( − 1 ) = 1 2 1 − ln ( A ) ---------------(1)
we can get the integral easily to be 2 4 ( ln ( 2 π ) + 1 ) − 2 1 ln ( A ) Note that the solution is not complete and the derivation of (1) is needed