21021031 has 4 divisors (see below), whose sum is σ = 21287200. Its totient is φ = 20754864.

The previous prime is 21021001. The next prime is 21021043. The reversal of 21021031 is 13012012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21021031 - 2²³ = 12632423 is a prime.

It is a super-2 number, since 2×21021031² = 883767488605922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21020999 and 21021017.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021001) 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, 132966 + ... + 133123.

It is an arithmetic number, because the mean of its divisors is an integer number (5321800).

Almost surely, 2^21021031 is an apocalyptic number.

21021031 is a deficient number, since it is larger than the sum of its proper divisors (266169).

21021031 is an equidigital number, since it uses as much as digits as its factorization.

21021031 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 266168.

The product of its (nonzero) digits is 12, while the sum is 10.

The square root of 21021031 is about 4584.8697909537. The cubic root of 21021031 is about 275.9844868057.

Adding to 21021031 its reverse (13012012), we get a palindrome (34033043).

The spelling of 21021031 in words is "twenty-one million, twenty-one thousand, thirty-one".