The ornamental design for a pentagonalbuildingblock, as shown and described.
FIG. 1 is a perspective view of a pentagonal building block, showing our new design;
FIG. 2 is a top plan view thereof, showing the vertical and horizontal symmetry of the design;
FIG. 3 is a bottom plan view thereof, which is a mirror image of the front elevation view;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a back elevation view thereof, which because of the vertical and horizontal symmetry of the design, is a mirror image of the front elevation view;
FIG. 6 is a left side elevation view thereof, which because of the vertical and horizontal symmetry of the design, is a rotation from the front elevation view; and,
FIG. 7 is a right side elevation view thereof, which because of the vertical and horizontal symmetry of the design, is a mirror image of the left side elevation view.