21605233 has 8 divisors (see below), whose sum is σ = 24018176. Its totient is φ = 19299600.

The previous prime is 21605209. The next prime is 21605251. The reversal of 21605233 is 33250612.

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

It is a cyclic number.

It is not a de Polignac number, because 21605233 - 2⁵ = 21605201 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21605263) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 26403 + ... + 27208.

It is an arithmetic number, because the mean of its divisors is an integer number (3002272).

Almost surely, 2^21605233 is an apocalyptic number.

It is an amenable number.

21605233 is a deficient number, since it is larger than the sum of its proper divisors (2412943).

21605233 is a wasteful number, since it uses less digits than its factorization.

21605233 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53655.

The product of its (nonzero) digits is 1080, while the sum is 22.

The square root of 21605233 is about 4648.1429625174. The cubic root of 21605233 is about 278.5178184178.

Adding to 21605233 its reverse (33250612), we get a palindrome (54855845).

The spelling of 21605233 in words is "twenty-one million, six hundred five thousand, two hundred thirty-three".