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<p>By definition:By <a href="page.php?w=M%C3%B6bius_inversion_formula">Möbius inversion</a>:</p>

<p><big>Series relations</big></p>
<p>Two <a href="page.php?w=Dirichlet_series">Dirichlet series</a> involving the divisor function are: </p>

<p>
:</p>

<p>where  is the <a href="page.php?w=Riemann_zeta_function">Riemann zeta function</a>. The series for d(n)&nbsp;=&nbsp;&sigma;<sub>0</sub>(n) gives: </p>

<p>
: </p>

<p>and a <a href="page.php?w=Ramanujan">Ramanujan</a> identity</p>

<p>
:</p>

<p>which is a special case of the <a href="page.php?w=Rankin-Selberg_method">Rankin-Selberg convolution</a>.</p><p>
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