21605385 has 32 divisors (see below), whose sum is σ = 36875520. Its totient is φ = 10764288.

The previous prime is 21605369. The next prime is 21605399. The reversal of 21605385 is 58350612.

It is not a de Polignac number, because 21605385 - 2⁴ = 21605369 is a prime.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 48996 + ... + 49434.

It is an arithmetic number, because the mean of its divisors is an integer number (1152360).

Almost surely, 2^21605385 is an apocalyptic number.

It is an amenable number.

21605385 is a deficient number, since it is larger than the sum of its proper divisors (15270135).

21605385 is a wasteful number, since it uses less digits than its factorization.

21605385 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 657.

The product of its (nonzero) digits is 7200, while the sum is 30.

The square root of 21605385 is about 4648.1593131045. The cubic root of 21605385 is about 278.5184715714.

Adding to 21605385 its reverse (58350612), we get a palindrome (79955997).

The spelling of 21605385 in words is "twenty-one million, six hundred five thousand, three hundred eighty-five".