The ornamental design for a pan, as shown and described.
FIG. 1 is a top, front, left perspective view of a pan showing my design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a cross section view taken from line 3-3 of FIG. 2;
FIG. 4 is a rear elevational view thereof; and,
FIG. 5 is an enlarged detail view of portion 5 shown in FIG. 3.
The broken lines in FIGS. 3 and 5 designating the enlarged view form no part of the claimed design. The remaining broken lines in the drawing views represent the portions of the pan that form no part of the claimed design.