21600021 has 4 divisors (see below), whose sum is σ = 28800032. Its totient is φ = 14400012.

The previous prime is 21600011. The next prime is 21600023. The reversal of 21600021 is 12000612.

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 21600021 - 2⁶ = 21599957 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21600023) 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, 3600001 + ... + 3600006.

It is an arithmetic number, because the mean of its divisors is an integer number (7200008).

Almost surely, 2^21600021 is an apocalyptic number.

It is an amenable number.

21600021 is a deficient number, since it is larger than the sum of its proper divisors (7200011).

21600021 is an equidigital number, since it uses as much as digits as its factorization.

21600021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7200010.

The product of its (nonzero) digits is 24, while the sum is 12.

The square root of 21600021 is about 4647.5822746886. The cubic root of 21600021 is about 278.4954202699.

Adding to 21600021 its reverse (12000612), we get a palindrome (33600633).

The spelling of 21600021 in words is "twenty-one million, six hundred thousand, twenty-one".