391721 has 8 divisors (see below), whose sum is σ = 432000. Its totient is φ = 352240.

The previous prime is 391717. The next prime is 391733. The reversal of 391721 is 127193.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 391721 - 2² = 391717 is a prime.

It is a Duffinian number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 391721.

It is not an unprimeable number, because it can be changed into a prime (391711) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1520 + ... + 1758.

It is an arithmetic number, because the mean of its divisors is an integer number (54000).

2³⁹¹⁷²¹ is an apocalyptic number.

It is an amenable number.

391721 is a deficient number, since it is larger than the sum of its proper divisors (40279).

391721 is a wasteful number, since it uses less digits than its factorization.

391721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 399.

The product of its digits is 378, while the sum is 23.

The square root of 391721 is about 625.8761858387. The cubic root of 391721 is about 73.1687470473.

The spelling of 391721 in words is "three hundred ninety-one thousand, seven hundred twenty-one".