721651 has 4 divisors (see below), whose sum is σ = 824752. Its totient is φ = 618552.

The previous prime is 721631. The next prime is 721661. The reversal of 721651 is 156127.

721651 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 721651 - 2⁵ = 721619 is a prime.

It is the 850-th Hogben number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (721621) by changing a digit.

It is a nontrivial repunit in base 849.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 51540 + ... + 51553.

It is an arithmetic number, because the mean of its divisors is an integer number (206188).

2⁷²¹⁶⁵¹ is an apocalyptic number.

721651 is a deficient number, since it is larger than the sum of its proper divisors (103101).

721651 is a wasteful number, since it uses less digits than its factorization.

721651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 103100.

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

The square root of 721651 is about 849.5004414360. The cubic root of 721651 is about 89.6965500343.

Adding to 721651 its reverse (156127), we get a palindrome (877778).

The spelling of 721651 in words is "seven hundred twenty-one thousand, six hundred fifty-one".