Divisor Sum Function/Table

Definition
The sequence of values of the sigma function for the first few positive integers begins:


 * $\begin{array} {r|r}

n & \map \sigma n \\ \hline 1 & 1 \\ 2 & 3 \\ 3 & 4 \\ 4 & 7 \\ 5 & 6 \\ 6 & 12 \\ 7 & 8 \\ 8 & 15 \\ 9 & 13 \\ 10 & 18 \\ 11 & 12 \\ 12 & 28 \\ 13 & 14 \\ 14 & 24 \\ 15 & 24 \\ 16 & 31 \end{array}$