21757221 has 32 divisors (see below), whose sum is σ = 34291200. Its totient is φ = 13608000.

The previous prime is 21757213. The next prime is 21757243. The reversal of 21757221 is 12275712.

It is not a de Polignac number, because 21757221 - 2³ = 21757213 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21757291) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 28596 + ... + 29346.

It is an arithmetic number, because the mean of its divisors is an integer number (1071600).

Almost surely, 2^21757221 is an apocalyptic number.

It is an amenable number.

21757221 is a deficient number, since it is larger than the sum of its proper divisors (12533979).

21757221 is a wasteful number, since it uses less digits than its factorization.

21757221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 826 (or 820 counting only the distinct ones).

The product of its digits is 1960, while the sum is 27.

The square root of 21757221 is about 4664.4636347602. The cubic root of 21757221 is about 279.1693964932.

The spelling of 21757221 in words is "twenty-one million, seven hundred fifty-seven thousand, two hundred twenty-one".