821720240 has 80 divisors (see below), whose sum is σ = 2093437440. Its totient is φ = 297480960.

The previous prime is 821720231. The next prime is 821720267. The reversal of 821720240 is 42027128.

821720240 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a tau number, because it is divible by the number of its divisors (80).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 208367 + ... + 212273.

It is an arithmetic number, because the mean of its divisors is an integer number (26167968).

Almost surely, 2^821720240 is an apocalyptic number.

821720240 is a gapful number since it is divisible by the number (80) 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 821720240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1046718720).

821720240 is an abundant number, since it is smaller than the sum of its proper divisors (1271717200).

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

821720240 is a wasteful number, since it uses less digits than its factorization.

821720240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4170 (or 4164 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 26.

The square root of 821720240 is about 28665.6630832081. The cubic root of 821720240 is about 936.6442286108.

Adding to 821720240 its reverse (42027128), we get a palindrome (863747368).

The spelling of 821720240 in words is "eight hundred twenty-one million, seven hundred twenty thousand, two hundred forty".