721615 has 4 divisors (see below), whose sum is σ = 865944. Its totient is φ = 577288.

The previous prime is 721613. The next prime is 721619. The reversal of 721615 is 516127.

721615 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It is a cyclic number.

It is not a de Polignac number, because 721615 - 2¹ = 721613 is a prime.

It is a Smith number, since the sum of its digits (22) 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.

721615 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721613) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 72157 + ... + 72166.

It is an arithmetic number, because the mean of its divisors is an integer number (216486).

2⁷²¹⁶¹⁵ is an apocalyptic number.

721615 is a deficient number, since it is larger than the sum of its proper divisors (144329).

721615 is a wasteful number, since it uses less digits than its factorization.

721615 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 144328.

The product of its digits is 420, while the sum is 22.

The square root of 721615 is about 849.4792522481. The cubic root of 721615 is about 89.6950584872.

The spelling of 721615 in words is "seven hundred twenty-one thousand, six hundred fifteen".