21605213 has 8 divisors (see below), whose sum is σ = 24936960. Its totient is φ = 18334800.

The previous prime is 21605209. The next prime is 21605251. The reversal of 21605213 is 31250612.

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 21605213 - 2² = 21605209 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21605263) 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, 14573 + ... + 15986.

It is an arithmetic number, because the mean of its divisors is an integer number (3117120).

Almost surely, 2^21605213 is an apocalyptic number.

It is an amenable number.

21605213 is a deficient number, since it is larger than the sum of its proper divisors (3331747).

21605213 is a wasteful number, since it uses less digits than its factorization.

21605213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30667.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 21605213 is about 4648.1408111201. The cubic root of 21605213 is about 278.5177324763.

Adding to 21605213 its reverse (31250612), we get a palindrome (52855825).

The spelling of 21605213 in words is "twenty-one million, six hundred five thousand, two hundred thirteen".