821

This number is a prime.

Just showing those entries submitted by 'Post': (Click here to show all)

The smallest of the prime quadruplet which is the largest of the three 3-digit prime quadruplets {101, 103, 107, 109}, {191, 193, 197, 199} and {821, 823, 827, 829} has, as digital reversal, the number of 6-digit prime quadruplets (128). [Post]

Smallest multidigit prime partial sum of number of planar graphs with minimum degree at least 1 and n nodes. Also largest known prime of its form: 0 + 1 + 2 + 7 + 22 + 109 + 680 = 821 is prime. [Post]