120

This number is a composite.

The decimal value of the fraction 135803690233087629631/135665296433469, to 120 digits, is 1001020.11202022102022102111203011122011203012102121102121103012112011302012112021103111103111112021202013102021202111113. Note that the 2nd, 3rd, 5th, 7th, 11th... digits are zeros. In fact, this 120-digit string has a 0 precisely in those positions corresponding to a prime number. This fraction has just 36 digits, yet its decimal value correctly encodes the primeness of the first 120 integers. Also note that 122223333432100/122098779 + 1/(10^7 - 1) gives the same 120-digit decimal, and uses only 29 digits. [Keith]