The ornamental design for a penta-lobed gas burner, as shown and described.
FIG. 1 is a top view of the penta-lobed gas burner;
FIG. 2 is a bottom view thereof;
FIG. 3 is a representative side view thereof, the other side views being substantially identical by virtue of the design's five-fold rotational symmetry; and,
FIG. 4 is a perspective view thereof.
For each such figure gas vent holes, where visible, are shown in broken lines for illustrative purposes only, and the pattern, size, and number of such holes form no part of the claimed design.