231705721 has 4 divisors (see below), whose sum is σ = 249529252. Its totient is φ = 213882192.

The previous prime is 231705689. The next prime is 231705757. The reversal of 231705721 is 127507132.

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 45765225 + 185940496 = 6765^2 + 13636^2 .

It is a cyclic number.

It is not a de Polignac number, because 231705721 - 2⁵ = 231705689 is a prime.

It is a super-2 number, since 2×231705721² = 107375082288259682, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 231705721.

It is not an unprimeable number, because it can be changed into a prime (231703721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8911746 + ... + 8911771.

It is an arithmetic number, because the mean of its divisors is an integer number (62382313).

Almost surely, 2^231705721 is an apocalyptic number.

It is an amenable number.

231705721 is a deficient number, since it is larger than the sum of its proper divisors (17823531).

231705721 is a wasteful number, since it uses less digits than its factorization.

231705721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17823530.

The product of its (nonzero) digits is 2940, while the sum is 28.

The square root of 231705721 is about 15221.8829649948. The cubic root of 231705721 is about 614.2034510949.

The spelling of 231705721 in words is "two hundred thirty-one million, seven hundred five thousand, seven hundred twenty-one".