21754721 has 4 divisors (see below), whose sum is σ = 21898944. Its totient is φ = 21610500.

The previous prime is 21754717. The next prime is 21754729. The reversal of 21754721 is 12745712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21754721 - 2² = 21754717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21754729) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 71885 + ... + 72186.

It is an arithmetic number, because the mean of its divisors is an integer number (5474736).

Almost surely, 2^21754721 is an apocalyptic number.

It is an amenable number.

21754721 is a deficient number, since it is larger than the sum of its proper divisors (144223).

21754721 is a wasteful number, since it uses less digits than its factorization.

21754721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 144222.

The product of its digits is 3920, while the sum is 29.

The square root of 21754721 is about 4664.1956434095. The cubic root of 21754721 is about 279.1587034881.

Subtracting from 21754721 its reverse (12745712), we obtain a palindrome (9009009).

The spelling of 21754721 in words is "twenty-one million, seven hundred fifty-four thousand, seven hundred twenty-one".