1181

This number is a prime.

+ The smallest reflectable invertible prime and also the smallest reflectable invertible emirp. [Capelle]

+ The smallest invertible dihedral prime, the smallest dihedral emirp, the smallest reflectable invertible dihedral prime, the smallest reflectable dihedral emirp, the smallest invertible dihedral emirp and also the smallest reflectable invertible dihedral emirp. Note that a dihedral prime is an emirp iff it is invertible. [Capelle]

+ 1181 a prime whose two first digits form the number ll and whose sum digits is ll. It equals the sum of the first ll primes primes with the end-digit l. The first of these primes is ll and the last one ends in ll. [Silva]

+ The minimal number of people ensuring, with better than even odds, that ten of them share a common birthday is an emirp. [Beedassy]

+ The sum of first 11 primes ending with 1 is an invertible emirp beginning with 11, (the smallest strobogrammatic prime), i.e., 11+31+41+61+71+101+131+151+181+191+211=1181. [Loungrides]

+ The smallest invertible prime p such that placing each digit d from p in the function (2^d + 1) always produces a prime. Note that the concatenation of the four primes thus produced {3||3||257||3} is an emirp. [Bajpai]

+ 1181 can be represented as the product of the first four odd primes plus the sum of the first four odd primes. [Akash]

+ In 1181, a supernova was observed by Chinese astronomers in the constellation now known as Cassiopeia. [Lowe]

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