21705456 has 80 divisors (see below), whose sum is σ = 59996160. Its totient is φ = 6746880.

The previous prime is 21705433. The next prime is 21705469. The reversal of 21705456 is 65450712.

It is a super-2 number, since 2×21705456² = 942253640335872, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 42901 + ... + 43403.

It is an arithmetic number, because the mean of its divisors is an integer number (749952).

Almost surely, 2^21705456 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 21705456, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29998080).

21705456 is an abundant number, since it is smaller than the sum of its proper divisors (38290704).

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

21705456 is a wasteful number, since it uses less digits than its factorization.

21705456 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 574 (or 568 counting only the distinct ones).

The product of its (nonzero) digits is 8400, while the sum is 30.

The square root of 21705456 is about 4658.9114608458. The cubic root of 21705456 is about 278.9478197915.

It can be divided in two parts, 2170 and 5456, that added together give a triangular number (7626 = T₁₂₃).

The spelling of 21705456 in words is "twenty-one million, seven hundred five thousand, four hundred fifty-six".