21664069 has 16 divisors (see below), whose sum is σ = 26345088. Its totient is φ = 17390592.

The previous prime is 21664067. The next prime is 21664081. The reversal of 21664069 is 96046612.

It is not a de Polignac number, because 21664069 - 2¹ = 21664067 is a prime.

It is a super-2 number, since 2×21664069² = 938663771273522, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664063) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 36237 + ... + 36829.

It is an arithmetic number, because the mean of its divisors is an integer number (1646568).

Almost surely, 2^21664069 is an apocalyptic number.

It is an amenable number.

21664069 is a deficient number, since it is larger than the sum of its proper divisors (4681019).

21664069 is a wasteful number, since it uses less digits than its factorization.

21664069 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 924.

The product of its (nonzero) digits is 15552, while the sum is 34.

The square root of 21664069 is about 4654.4676387316. The cubic root of 21664069 is about 278.7704118791.

The spelling of 21664069 in words is "twenty-one million, six hundred sixty-four thousand, sixty-nine".