721840 has 40 divisors (see below), whose sum is σ = 1919520. Its totient is φ = 247296.

The previous prime is 721793. The next prime is 721843. The reversal of 721840 is 48127.

It is a tau number, because it is divible by the number of its divisors (40).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721843) by changing a digit.

721840 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 7 ways as a sum of consecutive naturals, for example, 85 + ... + 1204.

It is an arithmetic number, because the mean of its divisors is an integer number (47988).

2⁷²¹⁸⁴⁰ is an apocalyptic number.

721840 is a gapful number since it is divisible by the number (70) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 721840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (959760).

721840 is an abundant number, since it is smaller than the sum of its proper divisors (1197680).

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

721840 is a wasteful number, since it uses less digits than its factorization.

721840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1309 (or 1303 counting only the distinct ones).

The product of its (nonzero) digits is 448, while the sum is 22.

The square root of 721840 is about 849.6116760026. The cubic root of 721840 is about 89.7043798432.

Adding to 721840 its reverse (48127), we get a palindrome (769967).

The spelling of 721840 in words is "seven hundred twenty-one thousand, eight hundred forty".