391968721 has 4 divisors (see below), whose sum is σ = 392152932. Its totient is φ = 391784512.

The previous prime is 391968719. The next prime is 391968749. The reversal of 391968721 is 127869193.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 72846225 + 319122496 = 8535^2 + 17864^2 .

It is a cyclic number.

It is not a de Polignac number, because 391968721 - 2¹ = 391968719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (391968701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 88876 + ... + 93181.

It is an arithmetic number, because the mean of its divisors is an integer number (98038233).

Almost surely, 2^391968721 is an apocalyptic number.

It is an amenable number.

391968721 is a deficient number, since it is larger than the sum of its proper divisors (184211).

391968721 is a wasteful number, since it uses less digits than its factorization.

391968721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 184210.

The product of its digits is 163296, while the sum is 46.

The square root of 391968721 is about 19798.1999434292. The cubic root of 391968721 is about 731.8416755985.

The spelling of 391968721 in words is "three hundred ninety-one million, nine hundred sixty-eight thousand, seven hundred twenty-one".