21697931 has 4 divisors (see below), whose sum is σ = 21912864. Its totient is φ = 21483000.

The previous prime is 21697927. The next prime is 21697937. The reversal of 21697931 is 13979612.

It is a happy number.

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 21697931 - 2² = 21697927 is a prime.

It is a super-2 number, since 2×21697931² = 941600419361522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21697937) 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, 107315 + ... + 107516.

It is an arithmetic number, because the mean of its divisors is an integer number (5478216).

Almost surely, 2^21697931 is an apocalyptic number.

21697931 is a deficient number, since it is larger than the sum of its proper divisors (214933).

21697931 is a wasteful number, since it uses less digits than its factorization.

21697931 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 214932.

The product of its digits is 20412, while the sum is 38.

The square root of 21697931 is about 4658.1037987576. The cubic root of 21697931 is about 278.9155802022.

The spelling of 21697931 in words is "twenty-one million, six hundred ninety-seven thousand, nine hundred thirty-one".