A Contour–Integral Representation for the *n*-th Prime

We derive a closed‐form analytic representation of the *n*-th prime number $p_n$, valid for all integers $n\ge 2$. The expression consists of a finite elementary backbone followed by a single Mellin–Barnes contour integral whose residues reproduce the classical asymptotic series obtained by inverting the logarithmic integral. Central to the construction is a factorial–free formula for the inversion coefficients $A_k$, expressed in terms of the polylogarithm $\operatorname{Li}_2$ and the gamma function. The divergent remainder of the standard expansion is resummed *via* Borel‐ Mellin techniques, yielding an exact identity rather than an asymptotic equality. Numerical evidence confirms that truncating the contour integral at its first residue already improves the relative error below 0.2 % for $n\gtrsim10^5$.

Publication Details

Journal
Figshare
Published
2025-01-01
DOI
https://doi.org/10.6084/m9.figshare.29310545.v1
Primary Topic
Analytic Number Theory Research
Type
article
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A Contour–Integral Representation for the *n*-th Prime

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Analytic Number Theory Research
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A Contour–Integral Representation for the *n*-th Prime

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Abstract

We derive a closed‐form analytic representation of the *n*-th prime number $p_n$, valid for all integers $n\ge 2$. The expression consists of a finite elementary backbone followed by a single Mellin–Barnes contour integral whose residues reproduce the classical asymptotic series obtained by inverting the logarithmic integral. Central to the construction is a factorial–free formula for the inversion coefficients $A_k$, expressed in terms of the polylogarithm $\operatorname{Li}_2$ and the gamma function. The divergent remainder of the standard expansion is resummed *via* Borel‐ Mellin techniques, yielding an exact identity rather than an asymptotic equality. Numerical evidence confirms that truncating the contour integral at its first residue already improves the relative error below 0.2 % for $n\gtrsim10^5$.

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Analytic Number Theory Research
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A Contour–Integral Representation for the *n*-th Prime · Figshare (2025) | TGRS Research Map | TGRS