21644769 has 8 divisors (see below), whose sum is σ = 29473920. Its totient is φ = 14122736.

The previous prime is 21644747. The next prime is 21644801. The reversal of 21644769 is 96744612.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21644769 - 2⁷ = 21644641 is a prime.

It is a super-2 number, since 2×21644769² = 936992050126722, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21644669) 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 7 ways as a sum of consecutive naturals, for example, 76614 + ... + 76895.

It is an arithmetic number, because the mean of its divisors is an integer number (3684240).

Almost surely, 2^21644769 is an apocalyptic number.

It is an amenable number.

21644769 is a deficient number, since it is larger than the sum of its proper divisors (7829151).

21644769 is a wasteful number, since it uses less digits than its factorization.

21644769 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 153559.

The product of its digits is 72576, while the sum is 39.

The square root of 21644769 is about 4652.3938999186. The cubic root of 21644769 is about 278.6876039902.

Adding to 21644769 its product of digits (72576), we get a triangular number (21717345 = T₆₅₉₀).

The spelling of 21644769 in words is "twenty-one million, six hundred forty-four thousand, seven hundred sixty-nine".