21705072 has 60 divisors (see below), whose sum is σ = 57686040. Its totient is φ = 7032320.

The previous prime is 21705071. The next prime is 21705083. The reversal of 21705072 is 27050712.

It is a super-2 number, since 2×21705072² = 942220301050368, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21705071) 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 11 ways as a sum of consecutive naturals, for example, 80554 + ... + 80822.

It is an arithmetic number, because the mean of its divisors is an integer number (961434).

Almost surely, 2^21705072 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 21705072, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28843020).

21705072 is an abundant number, since it is smaller than the sum of its proper divisors (35980968).

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

21705072 is a wasteful number, since it uses less digits than its factorization.

21705072 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 362 (or 315 counting only the distinct ones).

The product of its (nonzero) digits is 980, while the sum is 24.

The square root of 21705072 is about 4658.8702493201. The cubic root of 21705072 is about 278.9461747889.

Adding to 21705072 its reverse (27050712), we get a palindrome (48755784).

The spelling of 21705072 in words is "twenty-one million, seven hundred five thousand, seventy-two".