21664001 has 4 divisors (see below), whose sum is σ = 22938372. Its totient is φ = 20389632.

The previous prime is 21663997. The next prime is 21664007. The reversal of 21664001 is 10046612.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8151025 + 13512976 = 2855^2 + 3676^2 .

It is a cyclic number.

It is not a de Polignac number, because 21664001 - 2² = 21663997 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21664007) 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, 637160 + ... + 637193.

It is an arithmetic number, because the mean of its divisors is an integer number (5734593).

Almost surely, 2^21664001 is an apocalyptic number.

It is an amenable number.

21664001 is a deficient number, since it is larger than the sum of its proper divisors (1274371).

21664001 is a wasteful number, since it uses less digits than its factorization.

21664001 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1274370.

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 21664001 is about 4654.4603339163. The cubic root of 21664001 is about 278.7701202071.

The spelling of 21664001 in words is "twenty-one million, six hundred sixty-four thousand, one".