21021243 has 4 divisors (see below), whose sum is σ = 28028328. Its totient is φ = 14014160.

The previous prime is 21021229. The next prime is 21021251. The reversal of 21021243 is 34212012.

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

It is a cyclic number.

It is not a de Polignac number, because 21021243 - 2¹⁶ = 20955707 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21021263) 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, 3503538 + ... + 3503543.

It is an arithmetic number, because the mean of its divisors is an integer number (7007082).

Almost surely, 2^21021243 is an apocalyptic number.

21021243 is a deficient number, since it is larger than the sum of its proper divisors (7007085).

21021243 is an equidigital number, since it uses as much as digits as its factorization.

21021243 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7007084.

The product of its (nonzero) digits is 96, while the sum is 15.

The square root of 21021243 is about 4584.8929104179. The cubic root of 21021243 is about 275.9854145832.

Adding to 21021243 its reverse (34212012), we get a palindrome (55233255).

The spelling of 21021243 in words is "twenty-one million, twenty-one thousand, two hundred forty-three".