21708840 has 32 divisors (see below), whose sum is σ = 65126880. Its totient is φ = 5788992.

The previous prime is 21708821. The next prime is 21708857. The reversal of 21708840 is 4880712.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 21708798 and 21708807.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 90334 + ... + 90573.

It is an arithmetic number, because the mean of its divisors is an integer number (2035215).

Almost surely, 2^21708840 is an apocalyptic number.

21708840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21708840 is an abundant number, since it is smaller than the sum of its proper divisors (43418040).

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

21708840 is a wasteful number, since it uses less digits than its factorization.

21708840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 180921 (or 180917 counting only the distinct ones).

The product of its (nonzero) digits is 3584, while the sum is 30.

The square root of 21708840 is about 4659.2746216552. The cubic root of 21708840 is about 278.9623155381.

The spelling of 21708840 in words is "twenty-one million, seven hundred eight thousand, eight hundred forty".