21575721 has 16 divisors (see below), whose sum is σ = 30002688. Its totient is φ = 13776000.

The previous prime is 21575677. The next prime is 21575747. The reversal of 21575721 is 12757512.

It is not a de Polignac number, because 21575721 - 2⁶ = 21575657 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21575791) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8245 + ... + 10541.

It is an arithmetic number, because the mean of its divisors is an integer number (1875168).

Almost surely, 2^21575721 is an apocalyptic number.

It is an amenable number.

21575721 is a deficient number, since it is larger than the sum of its proper divisors (8426967).

21575721 is a wasteful number, since it uses less digits than its factorization.

21575721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2432.

The product of its digits is 4900, while the sum is 30.

The square root of 21575721 is about 4644.9672765263. The cubic root of 21575721 is about 278.3909454009.

The spelling of 21575721 in words is "twenty-one million, five hundred seventy-five thousand, seven hundred twenty-one".