21157205 has 8 divisors (see below), whose sum is σ = 25413504. Its totient is φ = 16909200.

The previous prime is 21157139. The next prime is 21157207. The reversal of 21157205 is 50275112.

It is a happy number.

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

It is not a de Polignac number, because 21157205 - 2¹⁰ = 21156181 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 (21157207) 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, 8000 + ... + 10310.

It is an arithmetic number, because the mean of its divisors is an integer number (3176688).

Almost surely, 2^21157205 is an apocalyptic number.

It is an amenable number.

21157205 is a deficient number, since it is larger than the sum of its proper divisors (4256299).

21157205 is a wasteful number, since it uses less digits than its factorization.

21157205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4147.

The product of its (nonzero) digits is 700, while the sum is 23.

The square root of 21157205 is about 4599.6961856192. The cubic root of 21157205 is about 276.5791460397.

The spelling of 21157205 in words is "twenty-one million, one hundred fifty-seven thousand, two hundred five".