11213

This number is a prime.

The Mathematics Department at the University of Illinois had their postage meter changed to stamp "2¹¹²¹³ - 1 IS PRIME" after a record-breaking Mersenne prime was found there in 1963.

The smallest prime formed by inserting the same digit in between three successive numbers. [Loungrides]

The smallest prime p formed by inserting a prime digit between the first double-digit twin prime pair. Curiously, sod(p) is a perfect cube. [Bajpai]