721345 has 8 divisors (see below), whose sum is σ = 875880. Its totient is φ = 570240.

The previous prime is 721337. The next prime is 721351. The reversal of 721345 is 543127.

It can be written as a sum of positive squares in 4 ways, for example, as 62001 + 659344 = 249^2 + 812^2 .

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

It is not a de Polignac number, because 721345 - 2³ = 721337 is a prime.

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 366 + ... + 1255.

It is an arithmetic number, because the mean of its divisors is an integer number (109485).

2⁷²¹³⁴⁵ is an apocalyptic number.

It is an amenable number.

721345 is a deficient number, since it is larger than the sum of its proper divisors (154535).

721345 is a wasteful number, since it uses less digits than its factorization.

721345 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1715.

The product of its digits is 840, while the sum is 22.

The square root of 721345 is about 849.3203164884. The cubic root of 721345 is about 89.6838703019.

The spelling of 721345 in words is "seven hundred twenty-one thousand, three hundred forty-five".