21051021 has 4 divisors (see below), whose sum is σ = 28068032. Its totient is φ = 14034012.

The previous prime is 21051011. The next prime is 21051029. The reversal of 21051021 is 12015012.

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 21051021 - 2⁹ = 21050509 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21050988 and 21051006.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21051029) 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, 3508501 + ... + 3508506.

It is an arithmetic number, because the mean of its divisors is an integer number (7017008).

Almost surely, 2^21051021 is an apocalyptic number.

It is an amenable number.

21051021 is a deficient number, since it is larger than the sum of its proper divisors (7017011).

21051021 is an equidigital number, since it uses as much as digits as its factorization.

21051021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7017010.

The product of its (nonzero) digits is 20, while the sum is 12.

The square root of 21051021 is about 4588.1391652826. The cubic root of 21051021 is about 276.1156703779.

Adding to 21051021 its reverse (12015012), we get a palindrome (33066033).

The spelling of 21051021 in words is "twenty-one million, fifty-one thousand, twenty-one".