21705540 has 96 divisors (see below), whose sum is σ = 63866880. Its totient is φ = 5502336.

The previous prime is 21705539. The next prime is 21705547. The reversal of 21705540 is 4550712.

It is a super-2 number, since 2×21705540² = 942260933383200, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21705540.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21705547) 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 31 ways as a sum of consecutive naturals, for example, 121171 + ... + 121349.

It is an arithmetic number, because the mean of its divisors is an integer number (665280).

Almost surely, 2^21705540 is an apocalyptic number.

21705540 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 21705540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31933440).

21705540 is an abundant number, since it is smaller than the sum of its proper divisors (42161340).

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

21705540 is a wasteful number, since it uses less digits than its factorization.

21705540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 281 (or 279 counting only the distinct ones).

The product of its (nonzero) digits is 1400, while the sum is 24.

The square root of 21705540 is about 4658.9204758184. The cubic root of 21705540 is about 278.9481796333.

The spelling of 21705540 in words is "twenty-one million, seven hundred five thousand, five hundred forty".