21297831 has 8 divisors (see below), whose sum is σ = 28519920. Its totient is φ = 14137152.

The previous prime is 21297817. The next prime is 21297851. The reversal of 21297831 is 13879212.

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

It is not a de Polignac number, because 21297831 - 2⁶ = 21297767 is a prime.

It is a super-2 number, since 2×21297831² = 907195210609122, which contains 22 as substring.

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a junction number, because it is equal to n+sod(n) for n = 21297792 and 21297801.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21297811) 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, 14536 + ... + 15933.

It is an arithmetic number, because the mean of its divisors is an integer number (3564990).

Almost surely, 2^21297831 is an apocalyptic number.

21297831 is a deficient number, since it is larger than the sum of its proper divisors (7222089).

21297831 is a wasteful number, since it uses less digits than its factorization.

21297831 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30705.

The product of its digits is 6048, while the sum is 33.

The square root of 21297831 is about 4614.9573129120. The cubic root of 21297831 is about 277.1905746729.

The spelling of 21297831 in words is "twenty-one million, two hundred ninety-seven thousand, eight hundred thirty-one".