20931691 has 4 divisors (see below), whose sum is σ = 22834584. Its totient is φ = 19028800.

The previous prime is 20931683. The next prime is 20931719. The reversal of 20931691 is 19613902.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20931691 - 2³ = 20931683 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20931191) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 951430 + ... + 951451.

It is an arithmetic number, because the mean of its divisors is an integer number (5708646).

Almost surely, 2^20931691 is an apocalyptic number.

20931691 is a deficient number, since it is larger than the sum of its proper divisors (1902893).

20931691 is a wasteful number, since it uses less digits than its factorization.

20931691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1902892.

The product of its (nonzero) digits is 2916, while the sum is 31.

The square root of 20931691 is about 4575.1165012489. The cubic root of 20931691 is about 275.5929508724.

The spelling of 20931691 in words is "twenty million, nine hundred thirty-one thousand, six hundred ninety-one".