21539440 has 80 divisors (see below), whose sum is σ = 54684000. Its totient is φ = 7842816.

The previous prime is 21539417. The next prime is 21539449. The reversal of 21539440 is 4493512.

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

It is a junction number, because it is equal to n+sod(n) for n = 21539399 and 21539408.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21539449) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 144486 + ... + 144634.

It is an arithmetic number, because the mean of its divisors is an integer number (683550).

Almost surely, 2^21539440 is an apocalyptic number.

21539440 is a gapful number since it is divisible by the number (20) 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 21539440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27342000).

21539440 is an abundant number, since it is smaller than the sum of its proper divisors (33144560).

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

21539440 is a wasteful number, since it uses less digits than its factorization.

21539440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 314 (or 308 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 21539440 is about 4641.0602236989. The cubic root of 21539440 is about 278.2348135985.

The spelling of 21539440 in words is "twenty-one million, five hundred thirty-nine thousand, four hundred forty".