721021 has 16 divisors (see below), whose sum is σ = 895104. Its totient is φ = 566784.

The previous prime is 721013. The next prime is 721037. The reversal of 721021 is 120127.

It is a cyclic number.

It is not a de Polignac number, because 721021 - 2³ = 721013 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 720992 and 721010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721051) 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, 8646 + ... + 8728.

It is an arithmetic number, because the mean of its divisors is an integer number (55944).

2⁷²¹⁰²¹ is an apocalyptic number.

It is an amenable number.

721021 is a deficient number, since it is larger than the sum of its proper divisors (174083).

721021 is a wasteful number, since it uses less digits than its factorization.

721021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 180.

The product of its (nonzero) digits is 28, while the sum is 13.

The square root of 721021 is about 849.1295543084. The cubic root of 721021 is about 89.6704407938.

Adding to 721021 its reverse (120127), we get a palindrome (841148).

The spelling of 721021 in words is "seven hundred twenty-one thousand, twenty-one", and thus it is an iban number.