720021 has 4 divisors (see below), whose sum is σ = 960032. Its totient is φ = 480012.

The previous prime is 720019. The next prime is 720023. The reversal of 720021 is 120027.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 120027 = 3 ⋅40009.

It is an interprime number because it is at equal distance from previous prime (720019) and next prime (720023).

It is not a de Polignac number, because 720021 - 2¹ = 720019 is a prime.

It is a D-number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 719979 and 720006.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (720023) 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, 120001 + ... + 120006.

It is an arithmetic number, because the mean of its divisors is an integer number (240008).

2⁷²⁰⁰²¹ is an apocalyptic number.

It is an amenable number.

720021 is a deficient number, since it is larger than the sum of its proper divisors (240011).

720021 is a wasteful number, since it uses less digits than its factorization.

720021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 240010.

The product of its (nonzero) digits is 28, while the sum is 12.

The square root of 720021 is about 848.5405117023. The cubic root of 720021 is about 89.6289663069.

Adding to 720021 its reverse (120027), we get a palindrome (840048).

The spelling of 720021 in words is "seven hundred twenty thousand, twenty-one", and thus it is an iban number.