109

This number is a prime.

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

109 = 1*2+3*4+5*6+7*8+9. [Silva]

The difference of the sum of the squares of the composite digits and the sum of the squares of the non-composite digits. [Silva]

The smallest prime of the form 10^(2k)+10^k-1. Those primes consist of 1 followed by k 0's and k 9's. [Silva]