821720 has 16 divisors (see below), whose sum is σ = 1848960. Its totient is φ = 328672.

The previous prime is 821677. The next prime is 821741. The reversal of 821720 is 27128.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 821692 and 821701.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10232 + ... + 10311.

It is an arithmetic number, because the mean of its divisors is an integer number (115560).

2⁸²¹⁷²⁰ is an apocalyptic number.

It is an amenable number.

821720 is an abundant number, since it is smaller than the sum of its proper divisors (1027240).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

821720 is a wasteful number, since it uses less digits than its factorization.

821720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20554 (or 20550 counting only the distinct ones).

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

The square root of 821720 is about 906.4877274404. The cubic root of 821720 is about 93.6644137422.

Adding to 821720 its reverse (27128), we get a palindrome (848848).

The spelling of 821720 in words is "eight hundred twenty-one thousand, seven hundred twenty".