21157221 has 8 divisors (see below), whose sum is σ = 29119744. Its totient is φ = 13649760.

The previous prime is 21157207. The next prime is 21157243. The reversal of 21157221 is 12275112.

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

It is not a de Polignac number, because 21157221 - 2¹⁴ = 21140837 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 (21157121) 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, 113656 + ... + 113841.

It is an arithmetic number, because the mean of its divisors is an integer number (3639968).

Almost surely, 2^21157221 is an apocalyptic number.

It is an amenable number.

21157221 is a deficient number, since it is larger than the sum of its proper divisors (7962523).

21157221 is a wasteful number, since it uses less digits than its factorization.

21157221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 227531.

The product of its digits is 280, while the sum is 21.

The square root of 21157221 is about 4599.6979248642. The cubic root of 21157221 is about 276.5792157601.

The spelling of 21157221 in words is "twenty-one million, one hundred fifty-seven thousand, two hundred twenty-one".