21351021 has 4 divisors (see below), whose sum is σ = 28468032. Its totient is φ = 14234012.

The previous prime is 21351017. The next prime is 21351053. The reversal of 21351021 is 12015312.

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 a cyclic number.

It is not a de Polignac number, because 21351021 - 2² = 21351017 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21351721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3558501 + ... + 3558506.

It is an arithmetic number, because the mean of its divisors is an integer number (7117008).

Almost surely, 2^21351021 is an apocalyptic number.

It is an amenable number.

21351021 is a deficient number, since it is larger than the sum of its proper divisors (7117011).

21351021 is an equidigital number, since it uses as much as digits as its factorization.

21351021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7117010.

The product of its (nonzero) digits is 60, while the sum is 15.

The square root of 21351021 is about 4620.7165028813. The cubic root of 21351021 is about 277.4211382107.

Adding to 21351021 its reverse (12015312), we get a palindrome (33366333).

It can be divided in two parts, 213510 and 21, that added together give a triangular number (213531 = T₆₅₃).

The spelling of 21351021 in words is "twenty-one million, three hundred fifty-one thousand, twenty-one".