21705880 has 32 divisors (see below), whose sum is σ = 55815840. Its totient is φ = 7441920.

The previous prime is 21705863. The next prime is 21705883. The reversal of 21705880 is 8850712.

It is a super-2 number, since 2×21705880² = 942290453148800, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21705883) 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, 38481 + ... + 39040.

It is an arithmetic number, because the mean of its divisors is an integer number (1744245).

Almost surely, 2^21705880 is an apocalyptic number.

21705880 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21705880 is an abundant number, since it is smaller than the sum of its proper divisors (34109960).

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

21705880 is a wasteful number, since it uses less digits than its factorization.

21705880 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 77539 (or 77535 counting only the distinct ones).

The product of its (nonzero) digits is 4480, while the sum is 31.

The square root of 21705880 is about 4658.9569648152. The cubic root of 21705880 is about 278.9496361260.

The spelling of 21705880 in words is "twenty-one million, seven hundred five thousand, eight hundred eighty".