21931021 has 8 divisors (see below), whose sum is σ = 25323200. Its totient is φ = 18603648.

The previous prime is 21931001. The next prime is 21931027. The reversal of 21931021 is 12013912.

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

It is not a de Polignac number, because 21931021 - 2⁷ = 21930893 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21931021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21931027) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15471 + ... + 16828.

It is an arithmetic number, because the mean of its divisors is an integer number (3165400).

Almost surely, 2^21931021 is an apocalyptic number.

It is an amenable number.

21931021 is a deficient number, since it is larger than the sum of its proper divisors (3392179).

21931021 is an equidigital number, since it uses as much as digits as its factorization.

21931021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32403.

The product of its (nonzero) digits is 108, while the sum is 19.

The square root of 21931021 is about 4683.0568008513. The cubic root of 21931021 is about 279.9107751420.

Adding to 21931021 its reverse (12013912), we get a palindrome (33944933).

The spelling of 21931021 in words is "twenty-one million, nine hundred thirty-one thousand, twenty-one".