821621440 has 56 divisors (see below), whose sum is σ = 1962649872. Its totient is φ = 327613440.

The previous prime is 821621357. The next prime is 821621447. The reversal of 821621440 is 44126128.

It is a junction number, because it is equal to n+sod(n) for n = 821621399 and 821621408.

It is not an unprimeable number, because it can be changed into a prime (821621447) 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, 102042 + ... + 109798.

Almost surely, 2^821621440 is an apocalyptic number.

821621440 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 821621440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (981324936).

821621440 is an abundant number, since it is smaller than the sum of its proper divisors (1141028432).

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

821621440 is a wasteful number, since it uses less digits than its factorization.

821621440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8105 (or 8095 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 28.

The square root of 821621440 is about 28663.9397152590. The cubic root of 821621440 is about 936.6066877891.

Adding to 821621440 its reverse (44126128), we get a palindrome (865747568).

The spelling of 821621440 in words is "eight hundred twenty-one million, six hundred twenty-one thousand, four hundred forty".