2139721 has 4 divisors (see below), whose sum is σ = 2143744. Its totient is φ = 2135700.

The previous prime is 2139691. The next prime is 2139733. The reversal of 2139721 is 1279312.

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 2139721 - 2¹¹ = 2137673 is a prime.

It is a Duffinian number.

2139721 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (2139521) 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, 1065 + ... + 2326.

It is an arithmetic number, because the mean of its divisors is an integer number (535936).

2^2139721 is an apocalyptic number.

It is an amenable number.

2139721 is a deficient number, since it is larger than the sum of its proper divisors (4023).

2139721 is an equidigital number, since it uses as much as digits as its factorization.

2139721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4022.

The product of its digits is 756, while the sum is 25.

The square root of 2139721 is about 1462.7785204876. The cubic root of 2139721 is about 128.8602737649.

The spelling of 2139721 in words is "two million, one hundred thirty-nine thousand, seven hundred twenty-one".