3999721 has 4 divisors (see below), whose sum is σ = 4363344. Its totient is φ = 3636100.

The previous prime is 3999719. The next prime is 3999727. The reversal of 3999721 is 1279993.

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 3999721 - 2¹ = 3999719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (3999727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 181795 + ... + 181816.

It is an arithmetic number, because the mean of its divisors is an integer number (1090836).

Almost surely, 2^3999721 is an apocalyptic number.

It is an amenable number.

3999721 is a deficient number, since it is larger than the sum of its proper divisors (363623).

3999721 is a wasteful number, since it uses less digits than its factorization.

3999721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 363622.

The product of its digits is 30618, while the sum is 40.

The square root of 3999721 is about 1999.9302487837. The cubic root of 3999721 is about 158.7364144036.

The spelling of 3999721 in words is "three million, nine hundred ninety-nine thousand, seven hundred twenty-one".