21573217 has 4 divisors (see below), whose sum is σ = 21728560. Its totient is φ = 21417876.

The previous prime is 21573203. The next prime is 21573239. The reversal of 21573217 is 71237512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21573217 - 2⁷ = 21573089 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21573317) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 77463 + ... + 77740.

It is an arithmetic number, because the mean of its divisors is an integer number (5432140).

Almost surely, 2^21573217 is an apocalyptic number.

It is an amenable number.

21573217 is a deficient number, since it is larger than the sum of its proper divisors (155343).

21573217 is a wasteful number, since it uses less digits than its factorization.

21573217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 155342.

The product of its digits is 2940, while the sum is 28.

The square root of 21573217 is about 4644.6977296698. The cubic root of 21573217 is about 278.3801753028.

The spelling of 21573217 in words is "twenty-one million, five hundred seventy-three thousand, two hundred seventeen".