21760021 has 4 divisors (see below), whose sum is σ = 22266112. Its totient is φ = 21253932.

The previous prime is 21760019. The next prime is 21760031. The reversal of 21760021 is 12006712.

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 21760021 - 2¹ = 21760019 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 (21760031) 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, 252981 + ... + 253066.

It is an arithmetic number, because the mean of its divisors is an integer number (5566528).

Almost surely, 2^21760021 is an apocalyptic number.

It is an amenable number.

21760021 is a deficient number, since it is larger than the sum of its proper divisors (506091).

21760021 is an equidigital number, since it uses as much as digits as its factorization.

21760021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 506090.

The product of its (nonzero) digits is 168, while the sum is 19.

The square root of 21760021 is about 4664.7637667946. The cubic root of 21760021 is about 279.1813716865.

Adding to 21760021 its reverse (12006712), we get a palindrome (33766733).

The spelling of 21760021 in words is "twenty-one million, seven hundred sixty thousand, twenty-one".