21968251 has 4 divisors (see below), whose sum is σ = 22504104. Its totient is φ = 21432400.

The previous prime is 21968239. The next prime is 21968257. The reversal of 21968251 is 15286912.

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 21968251 - 2⁹ = 21967739 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21968257) 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, 267865 + ... + 267946.

It is an arithmetic number, because the mean of its divisors is an integer number (5626026).

Almost surely, 2^21968251 is an apocalyptic number.

21968251 is a deficient number, since it is larger than the sum of its proper divisors (535853).

21968251 is an equidigital number, since it uses as much as digits as its factorization.

21968251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 535852.

The product of its digits is 8640, while the sum is 34.

The square root of 21968251 is about 4687.0300831123. The cubic root of 21968251 is about 280.0690773446.

The spelling of 21968251 in words is "twenty-one million, nine hundred sixty-eight thousand, two hundred fifty-one".