820721 has 4 divisors (see below), whose sum is σ = 895344. Its totient is φ = 746100.

The previous prime is 820711. The next prime is 820723. The reversal of 820721 is 127028.

820721 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, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 820721 - 2⁶ = 820657 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 820693 and 820702.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 820721.

It is not an unprimeable number, because it can be changed into a prime (820723) 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, 37295 + ... + 37316.

It is an arithmetic number, because the mean of its divisors is an integer number (223836).

2⁸²⁰⁷²¹ is an apocalyptic number.

It is an amenable number.

820721 is a deficient number, since it is larger than the sum of its proper divisors (74623).

820721 is a wasteful number, since it uses less digits than its factorization.

820721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 74622.

The product of its (nonzero) digits is 224, while the sum is 20.

The square root of 820721 is about 905.9365319933. The cubic root of 820721 is about 93.6264410774.

Adding to 820721 its reverse (127028), we get a palindrome (947749).

It can be divided in two parts, 8207 and 21, that added together give a palindrome (8228).

The spelling of 820721 in words is "eight hundred twenty thousand, seven hundred twenty-one".