21991917 has 8 divisors (see below), whose sum is σ = 29368224. Its totient is φ = 14638448.

The previous prime is 21991913. The next prime is 21991919. The reversal of 21991917 is 71919912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21991917 - 2² = 21991913 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21991913) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3318 + ... + 7415.

It is an arithmetic number, because the mean of its divisors is an integer number (3671028).

Almost surely, 2^21991917 is an apocalyptic number.

It is an amenable number.

21991917 is a deficient number, since it is larger than the sum of its proper divisors (7376307).

21991917 is a wasteful number, since it uses less digits than its factorization.

21991917 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11419.

The product of its digits is 10206, while the sum is 39.

The square root of 21991917 is about 4689.5540299692. The cubic root of 21991917 is about 280.1696123712.

The spelling of 21991917 in words is "twenty-one million, nine hundred ninety-one thousand, nine hundred seventeen".