21604385 has 8 divisors (see below), whose sum is σ = 28282176. Its totient is φ = 15712240.

The previous prime is 21604381. The next prime is 21604393. The reversal of 21604385 is 58340612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21604385 - 2² = 21604381 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21604381) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 196349 + ... + 196458.

It is an arithmetic number, because the mean of its divisors is an integer number (3535272).

Almost surely, 2^21604385 is an apocalyptic number.

It is an amenable number.

21604385 is a deficient number, since it is larger than the sum of its proper divisors (6677791).

21604385 is a wasteful number, since it uses less digits than its factorization.

21604385 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 392823.

The product of its (nonzero) digits is 5760, while the sum is 29.

The square root of 21604385 is about 4648.0517423970. The cubic root of 21604385 is about 278.5141744518.

Adding to 21604385 its reverse (58340612), we get a palindrome (79944997).

It can be divided in two parts, 21 and 604385, that added together give a palindrome (604406).

The spelling of 21604385 in words is "twenty-one million, six hundred four thousand, three hundred eighty-five".