211691 has 2 divisors, whose sum is σ = 211692. Its totient is φ = 211690.

The previous prime is 211681. The next prime is 211693. The reversal of 211691 is 196112.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-211691 is a prime.

Together with 211693, it forms a pair of twin primes.

It is a Chen prime.

It is an Ulam number.

It is not a weakly prime, because it can be changed into another prime (211693) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 105845 + 105846.

It is an arithmetic number, because the mean of its divisors is an integer number (105846).

2²¹¹⁶⁹¹ is an apocalyptic number.

211691 is a deficient number, since it is larger than the sum of its proper divisors (1).

211691 is an equidigital number, since it uses as much as digits as its factorization.

211691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 108, while the sum is 20.

The square root of 211691 is about 460.0989024112. The cubic root of 211691 is about 59.5983356141.

It can be divided in two parts, 21 and 1691, that multiplied together give a triangular number (35511 = T₂₆₆).

The spelling of 211691 in words is "two hundred eleven thousand, six hundred ninety-one".