21953021 has 4 divisors (see below), whose sum is σ = 21966012. Its totient is φ = 21940032.

The previous prime is 21953011. The next prime is 21953033. The reversal of 21953021 is 12035912.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1792921 + 20160100 = 1339^2 + 4490^2 .

It is a cyclic number.

It is not a de Polignac number, because 21953021 - 2¹⁰ = 21951997 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 (21953011) 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, 3500 + ... + 7493.

It is an arithmetic number, because the mean of its divisors is an integer number (5491503).

Almost surely, 2^21953021 is an apocalyptic number.

It is an amenable number.

21953021 is a deficient number, since it is larger than the sum of its proper divisors (12991).

21953021 is a wasteful number, since it uses less digits than its factorization.

21953021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12990.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21953021 is about 4685.4051052177. The cubic root of 21953021 is about 280.0043409191.

Adding to 21953021 its reverse (12035912), we get a palindrome (33988933).

The spelling of 21953021 in words is "twenty-one million, nine hundred fifty-three thousand, twenty-one".