721957 has 4 divisors (see below), whose sum is σ = 728460. Its totient is φ = 715456.

The previous prime is 721951. The next prime is 721961. The reversal of 721957 is 759127.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 759127 = 73 ⋅10399.

It can be written as a sum of positive squares in 2 ways, for example, as 6241 + 715716 = 79^2 + 846^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-721957 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3082 + ... + 3307.

It is an arithmetic number, because the mean of its divisors is an integer number (182115).

2⁷²¹⁹⁵⁷ is an apocalyptic number.

It is an amenable number.

721957 is a deficient number, since it is larger than the sum of its proper divisors (6503).

721957 is a wasteful number, since it uses less digits than its factorization.

721957 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6502.

The product of its digits is 4410, while the sum is 31.

The square root of 721957 is about 849.6805281987. The cubic root of 721957 is about 89.7092261829.

The spelling of 721957 in words is "seven hundred twenty-one thousand, nine hundred fifty-seven".