273

This number is a composite.

The 273rd prime minus sum of gaps between the first 273 consecutive primes minus one equals 273. [Fentsor]

The smallest number n (a composite number) such that 10^n-n^10 is a prime. The next such number, also composite, is 399. [Loungrides]

The smallest of the only two sphenic numbers consisting of distinct prime digits. Note that its prime factors (3, 7, 13), concatenated in reverse order, is prime. [Loungrides]