21807997 has 4 divisors (see below), whose sum is σ = 21828096. Its totient is φ = 21787900.

The previous prime is 21807959. The next prime is 21808013. The reversal of 21807997 is 79970812.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21807997 - 2⁷ = 21807869 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21807917) 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, 8323 + ... + 10624.

It is an arithmetic number, because the mean of its divisors is an integer number (5457024).

Almost surely, 2^21807997 is an apocalyptic number.

It is an amenable number.

21807997 is a deficient number, since it is larger than the sum of its proper divisors (20099).

21807997 is a wasteful number, since it uses less digits than its factorization.

21807997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20098.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 21807997 is about 4669.9033180570. The cubic root of 21807997 is about 279.3863986628.

The spelling of 21807997 in words is "twenty-one million, eight hundred seven thousand, nine hundred ninety-seven".