21685860 has 96 divisors (see below), whose sum is σ = 77118720. Its totient is φ = 4955904.

The previous prime is 21685837. The next prime is 21685861. The reversal of 21685860 is 6858612.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (21685861) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 912 + ... + 6648.

It is an arithmetic number, because the mean of its divisors is an integer number (803320).

Almost surely, 2^21685860 is an apocalyptic number.

21685860 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 21685860, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38559360).

21685860 is an abundant number, since it is smaller than the sum of its proper divisors (55432860).

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

21685860 is a wasteful number, since it uses less digits than its factorization.

21685860 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5762 (or 5754 counting only the distinct ones).

The product of its (nonzero) digits is 23040, while the sum is 36.

The square root of 21685860 is about 4656.8079195947. The cubic root of 21685860 is about 278.8638484726.

The spelling of 21685860 in words is "twenty-one million, six hundred eighty-five thousand, eight hundred sixty".