21557984 has 48 divisors (see below), whose sum is σ = 48894048. Its totient is φ = 9165312.

The previous prime is 21557983. The next prime is 21558001. The reversal of 21557984 is 48975512.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21557983) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 34862 + ... + 35474.

It is an arithmetic number, because the mean of its divisors is an integer number (1018626).

Almost surely, 2^21557984 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21557984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24447024).

21557984 is an abundant number, since it is smaller than the sum of its proper divisors (27336064).

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

21557984 is a wasteful number, since it uses less digits than its factorization.

21557984 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 787 (or 779 counting only the distinct ones).

The product of its digits is 100800, while the sum is 41.

The square root of 21557984 is about 4643.0576132544. The cubic root of 21557984 is about 278.3146378094.

The spelling of 21557984 in words is "twenty-one million, five hundred fifty-seven thousand, nine hundred eighty-four".