I'm idly curious, but lack the gumption to calculate: What happens if you append on the left? 1 21 321 4321 54321 ... 10987654321 1110987654321 121110987654321 ... What happens if you reflect the numbers? 123456789101112 --> 211101987654321 121110987654321 --> 123456789011121 What's the least N for which all four are prime?