21031021 has 4 divisors (see below), whose sum is σ = 22942944. Its totient is φ = 19119100.

The previous prime is 21031019. The next prime is 21031027. The reversal of 21031021 is 12013012.

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 not a de Polignac number, because 21031021 - 2¹ = 21031019 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21030989 and 21031007.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21031027) 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 3 ways as a sum of consecutive naturals, for example, 955945 + ... + 955966.

It is an arithmetic number, because the mean of its divisors is an integer number (5735736).

Almost surely, 2^21031021 is an apocalyptic number.

It is an amenable number.

21031021 is a deficient number, since it is larger than the sum of its proper divisors (1911923).

21031021 is a wasteful number, since it uses less digits than its factorization.

21031021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1911922.

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

The square root of 21031021 is about 4585.9591145147. The cubic root of 21031021 is about 276.0281993522.

Adding to 21031021 its reverse (12013012), we get a palindrome (33044033).

Subtracting from 21031021 its reverse (12013012), we obtain a square (9018009 = 3003²).

The spelling of 21031021 in words is "twenty-one million, thirty-one thousand, twenty-one".