Spoiler: It's a smiley sun. The outside is fully symmetrical, the face isn't. For the outside 16 rays: The centre four 5s start at the edge. Each diagonal is 5 single squares, each starting 3 in from each corner (e.g. R3 C3). Then there are 8 2,1,2 rays (e.g. C8,R2/3 C9,R4 C10,R5/6) Reflect that round 7 times and there's the outside done!