thead><tr>
<th>
                  <p>
                    Function
                  </p>
                </th>
<th>
                  <p>
                    Implementation Notes
                  </p>
                </th>
</tr></thead>
<tbody>
<tr>
<td>
                  <p>
                    pdf
                  </p>
                </td>
<td>
                  <p>
                    pdf = exp(lgamma(r + k) - lgamma(r) - lgamma(k+1)) * pow(p, r)
                    * pow((1-p), k)
                  