21604640 has 24 divisors (see below), whose sum is σ = 51041340. Its totient is φ = 8641792.

The previous prime is 21604621. The next prime is 21604643. The reversal of 21604640 is 4640612.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 19678096 + 1926544 = 4436^2 + 1388^2 .

It is not an unprimeable number, because it can be changed into a prime (21604643) 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, 67355 + ... + 67674.

Almost surely, 2^21604640 is an apocalyptic number.

21604640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21604640 is an abundant number, since it is smaller than the sum of its proper divisors (29436700).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21604640 is a wasteful number, since it uses less digits than its factorization.

21604640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 135044 (or 135036 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 23.

The square root of 21604640 is about 4648.0791731639. The cubic root of 21604640 is about 278.5152702299.

The spelling of 21604640 in words is "twenty-one million, six hundred four thousand, six hundred forty".