FIG. 1 is a top view of the armchair embodying the inventive design; FIG. 2 is a rear view of the armchair embodying the inventive design; FIG. 3 is a front view of the armchair embodying the inventive design; FIG. 4 is a bottom view of the armchair embodying the inventive design; FIG. 5 is a left side view of the armchair embodying the inventive design; and, FIG. 6 is a right side view of the armchair embodying the inventive design. The broken lines shown are understood to represent stitching.