21644729 has 4 divisors (see below), whose sum is σ = 21854976. Its totient is φ = 21434484.

The previous prime is 21644717. The next prime is 21644731. The reversal of 21644729 is 92744612.

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 21644729 - 2⁴ = 21644713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21644429) 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, 104969 + ... + 105174.

It is an arithmetic number, because the mean of its divisors is an integer number (5463744).

Almost surely, 2^21644729 is an apocalyptic number.

It is an amenable number.

21644729 is a deficient number, since it is larger than the sum of its proper divisors (210247).

21644729 is a wasteful number, since it uses less digits than its factorization.

21644729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 210246.

The product of its digits is 24192, while the sum is 35.

The square root of 21644729 is about 4652.3896010545. The cubic root of 21644729 is about 278.6874323165.

The spelling of 21644729 in words is "twenty-one million, six hundred forty-four thousand, seven hundred twenty-nine".