I claim the ornamental design for an armchair, as shown and described.
FIG. 1 is a front perspective view of an armchair.
FIG. 2 is a right side view shown in FIG. 1.
FIG. 3 is a left side view shown in FIG. 1
FIG. 4 is a front view shown in FIG. 1
FIG. 5 is a top view shown in FIG. 1
FIG. 6 is a rear view shown in FIG. 1; and,
FIG. 7 is a bottom view shown in FIG. 1.
The short even dashed lines shown along the seam lines on the backrest and seat are understood to represent stitching.
The broken lines showing of the four circular members, beneath the armrest panels in FIGS. 2-7, are for illustrative purposes only and form no part of the claimed design.