21725021 has 4 divisors (see below), whose sum is σ = 21737052. Its totient is φ = 21712992.

The previous prime is 21725009. The next prime is 21725027. The reversal of 21725021 is 12052712.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 21576025 + 148996 = 4645^2 + 386^2 .

It is a cyclic number.

It is not a de Polignac number, because 21725021 - 2¹⁸ = 21462877 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21724984 and 21725002.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21725027) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2696 + ... + 7121.

It is an arithmetic number, because the mean of its divisors is an integer number (5434263).

Almost surely, 2^21725021 is an apocalyptic number.

It is an amenable number.

21725021 is a deficient number, since it is larger than the sum of its proper divisors (12031).

21725021 is an equidigital number, since it uses as much as digits as its factorization.

21725021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12030.

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 21725021 is about 4661.0107272994. The cubic root of 21725021 is about 279.0316078663.

Adding to 21725021 its reverse (12052712), we get a palindrome (33777733).

The spelling of 21725021 in words is "twenty-one million, seven hundred twenty-five thousand, twenty-one".