821555840 has 64 divisors (see below), whose sum is σ = 2244620160. Its totient is φ = 281674752.

The previous prime is 821555803. The next prime is 821555843. The reversal of 821555840 is 48555128.

821555840 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 (64).

It is a junction number, because it is equal to n+sod(n) for n = 821555794 and 821555803.

It is not an unprimeable number, because it can be changed into a prime (821555843) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 87212 + ... + 96171.

It is an arithmetic number, because the mean of its divisors is an integer number (35072190).

Almost surely, 2^821555840 is an apocalyptic number.

821555840 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

821555840 is an abundant number, since it is smaller than the sum of its proper divisors (1423064320).

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

821555840 is a wasteful number, since it uses less digits than its factorization.

821555840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 183409 (or 183397 counting only the distinct ones).

The product of its (nonzero) digits is 64000, while the sum is 38.

The square root of 821555840 is about 28662.7953975184. The cubic root of 821555840 is about 936.5817602369.

The spelling of 821555840 in words is "eight hundred twenty-one million, five hundred fifty-five thousand, eight hundred forty".