21604649 has 4 divisors (see below), whose sum is σ = 23568720. Its totient is φ = 19640580.

The previous prime is 21604643. The next prime is 21604669. The reversal of 21604649 is 94640612.

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 21604649 - 2⁸ = 21604393 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21604643) 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 3 ways as a sum of consecutive naturals, for example, 982019 + ... + 982040.

It is an arithmetic number, because the mean of its divisors is an integer number (5892180).

Almost surely, 2^21604649 is an apocalyptic number.

It is an amenable number.

21604649 is a deficient number, since it is larger than the sum of its proper divisors (1964071).

21604649 is a wasteful number, since it uses less digits than its factorization.

21604649 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1964070.

The product of its (nonzero) digits is 10368, while the sum is 32.

The square root of 21604649 is about 4648.0801413057. The cubic root of 21604649 is about 278.5153089043.

The spelling of 21604649 in words is "twenty-one million, six hundred four thousand, six hundred forty-nine".