16640021 has 4 divisors (see below), whose sum is σ = 16994112. Its totient is φ = 16285932.

The previous prime is 16640003. The next prime is 16640023. The reversal of 16640021 is 12004661.

It is a happy number.

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 16640021 - 2¹⁸ = 16377877 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 16639975 and 16640002.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16640023) 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, 176975 + ... + 177068.

It is an arithmetic number, because the mean of its divisors is an integer number (4248528).

Almost surely, 2^16640021 is an apocalyptic number.

It is an amenable number.

16640021 is a deficient number, since it is larger than the sum of its proper divisors (354091).

16640021 is an equidigital number, since it uses as much as digits as its factorization.

16640021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 354090.

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

The square root of 16640021 is about 4079.2181848977. The cubic root of 16640021 is about 255.3002793523.

Adding to 16640021 its reverse (12004661), we get a palindrome (28644682).

The spelling of 16640021 in words is "sixteen million, six hundred forty thousand, twenty-one".