21765021 has 4 divisors (see below), whose sum is σ = 29020032. Its totient is φ = 14510012.

The previous prime is 21765019. The next prime is 21765031. The reversal of 21765021 is 12056712.

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 21765021 - 2¹ = 21765019 is a prime.

It is a super-2 number, since 2×21765021² = 947432278260882, which contains 22 as substring.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21764982 and 21765000.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21765031) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3627501 + ... + 3627506.

It is an arithmetic number, because the mean of its divisors is an integer number (7255008).

Almost surely, 2^21765021 is an apocalyptic number.

It is an amenable number.

21765021 is a deficient number, since it is larger than the sum of its proper divisors (7255011).

21765021 is an equidigital number, since it uses as much as digits as its factorization.

21765021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7255010.

The product of its (nonzero) digits is 840, while the sum is 24.

The square root of 21765021 is about 4665.2996688316. The cubic root of 21765021 is about 279.2027534054.

The spelling of 21765021 in words is "twenty-one million, seven hundred sixty-five thousand, twenty-one".