21531797 has 4 divisors (see below), whose sum is σ = 24607776. Its totient is φ = 18455820.

The previous prime is 21531793. The next prime is 21531799. The reversal of 21531797 is 79713512.

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 21531797 - 2² = 21531793 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 (21531793) 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, 1537979 + ... + 1537992.

It is an arithmetic number, because the mean of its divisors is an integer number (6151944).

Almost surely, 2^21531797 is an apocalyptic number.

It is an amenable number.

21531797 is a deficient number, since it is larger than the sum of its proper divisors (3075979).

21531797 is an equidigital number, since it uses as much as digits as its factorization.

21531797 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3075978.

The product of its digits is 13230, while the sum is 35.

The square root of 21531797 is about 4640.2367396503. The cubic root of 21531797 is about 278.2019003278.

The spelling of 21531797 in words is "twenty-one million, five hundred thirty-one thousand, seven hundred ninety-seven".