721665723 has 16 divisors (see below), whose sum is σ = 1012336416. Its totient is φ = 456687360.

The previous prime is 721665719. The next prime is 721665727. The reversal of 721665723 is 327566127.

It is an interprime number because it is at equal distance from previous prime (721665719) and next prime (721665727).

It is not a de Polignac number, because 721665723 - 2² = 721665719 is a prime.

It is a super-2 number, since 2×721665723² = 1041602831506225458, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (721665727) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 74736 + ... + 83837.

It is an arithmetic number, because the mean of its divisors is an integer number (63271026).

Almost surely, 2^721665723 is an apocalyptic number.

721665723 is a deficient number, since it is larger than the sum of its proper divisors (290670693).

721665723 is a wasteful number, since it uses less digits than its factorization.

721665723 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 158654.

The product of its digits is 105840, while the sum is 39.

The square root of 721665723 is about 26863.8367140660. The cubic root of 721665723 is about 896.9716002139.

The spelling of 721665723 in words is "seven hundred twenty-one million, six hundred sixty-five thousand, seven hundred twenty-three".