21452721 has 32 divisors (see below), whose sum is σ = 31518720. Its totient is φ = 12936000.

The previous prime is 21452701. The next prime is 21452731. The reversal of 21452721 is 12725412.

It is not a de Polignac number, because 21452721 - 2⁹ = 21452209 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a junction number, because it is equal to n+sod(n) for n = 21452691 and 21452700.

It is not an unprimeable number, because it can be changed into a prime (21452701) 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, 141996 + ... + 142146.

It is an arithmetic number, because the mean of its divisors is an integer number (984960).

Almost surely, 2^21452721 is an apocalyptic number.

It is an amenable number.

21452721 is a deficient number, since it is larger than the sum of its proper divisors (10065999).

21452721 is a wasteful number, since it uses less digits than its factorization.

21452721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 277.

The product of its digits is 1120, while the sum is 24.

The square root of 21452721 is about 4631.7082161984. The cubic root of 21452721 is about 277.8609150202.

The spelling of 21452721 in words is "twenty-one million, four hundred fifty-two thousand, seven hundred twenty-one".