721820 has 48 divisors (see below), whose sum is σ = 1759968. Its totient is φ = 245760.

The previous prime is 721793. The next prime is 721843. The reversal of 721820 is 28127.

721820 = 198² + 199² + ... + 214².

It is a super-2 number, since 2×721820² = 1042048224800, which contains 22 as substring.

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 = 721792 and 721801.

It is a congruent number.

It is an unprimeable number.

721820 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3644 + ... + 3836.

It is an arithmetic number, because the mean of its divisors is an integer number (36666).

2⁷²¹⁸²⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 721820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (879984).

721820 is an abundant number, since it is smaller than the sum of its proper divisors (1038148).

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

721820 is a wasteful number, since it uses less digits than its factorization.

721820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 230 (or 228 counting only the distinct ones).

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

The square root of 721820 is about 849.5999058380. The cubic root of 721820 is about 89.7035513567.

Adding to 721820 its reverse (28127), we get a palindrome (749947).

The spelling of 721820 in words is "seven hundred twenty-one thousand, eight hundred twenty".