21739251 has 4 divisors (see below), whose sum is σ = 28985672. Its totient is φ = 14492832.

The previous prime is 21739247. The next prime is 21739261. The reversal of 21739251 is 15293712.

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

It is not a de Polignac number, because 21739251 - 2² = 21739247 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21739261) 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, 3623206 + ... + 3623211.

It is an arithmetic number, because the mean of its divisors is an integer number (7246418).

Almost surely, 2^21739251 is an apocalyptic number.

21739251 is a deficient number, since it is larger than the sum of its proper divisors (7246421).

21739251 is an equidigital number, since it uses as much as digits as its factorization.

21739251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7246420.

The product of its digits is 3780, while the sum is 30.

The square root of 21739251 is about 4662.5369703628. The cubic root of 21739251 is about 279.0925169469.

The spelling of 21739251 in words is "twenty-one million, seven hundred thirty-nine thousand, two hundred fifty-one".