Some recreational mathematicians call this sort of thing a "Digital Bracelet" because it's a circular arrangement of digits that has no clear beginning, end, or even direction. The digits 1, 9, 3, 9, 3, 9 can be progressively transposed to create a fluid circle of 6-digit prime numbers that works forward and backward.
You can start with any digit on this circle and move in either direction to generate a prime. The pattern is both simple and mathematically beautiful -- and THAT is why someone needs to make this into a necklace.
#vsauce #education #maths