821001440 has 144 divisors (see below), whose sum is σ = 2265078816. Its totient is φ = 275466240.

The previous prime is 821001437. The next prime is 821001443. The reversal of 821001440 is 44100128.

It is an interprime number because it is at equal distance from previous prime (821001437) and next prime (821001443).

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821001443) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4167422 + ... + 4167618.

It is an arithmetic number, because the mean of its divisors is an integer number (15729714).

Almost surely, 2^821001440 is an apocalyptic number.

821001440 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 821001440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1132539408).

821001440 is an abundant number, since it is smaller than the sum of its proper divisors (1444077376).

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

821001440 is a wasteful number, since it uses less digits than its factorization.

821001440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 341 (or 272 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 20.

The square root of 821001440 is about 28653.1226919510. The cubic root of 821001440 is about 936.3710390078.

Adding to 821001440 its reverse (44100128), we get a palindrome (865101568).

The spelling of 821001440 in words is "eight hundred twenty-one million, one thousand, four hundred forty".