The ornamental design for an armchair, as shown and described.
FIG. 1 is a side perspective view of an armchair showing my design;
FIG. 2 is a front perspective view;
FIG. 3 is a rear perspective view; and
FIG. 4 is a top view thereof.
The chair is characterized by the backrest including a vertical central
scored panel spaced from vertical end bars in combination with the
laterally extending V-shaped rear leg members and the scored seat portion
all as best illustrated in FIGS. 1, 3, and 4.