21685680 has 60 divisors (see below), whose sum is σ = 72830160. Its totient is φ = 5782656.

The previous prime is 21685667. The next prime is 21685687. The reversal of 21685680 is 8658612.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (60).

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21685687) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14340 + ... + 15779.

It is an arithmetic number, because the mean of its divisors is an integer number (1213836).

Almost surely, 2^21685680 is an apocalyptic number.

21685680 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21685680 is an abundant number, since it is smaller than the sum of its proper divisors (51144480).

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

21685680 is a wasteful number, since it uses less digits than its factorization.

21685680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30138 (or 30129 counting only the distinct ones).

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

The square root of 21685680 is about 4656.7885930113. The cubic root of 21685680 is about 278.8630769155.

The spelling of 21685680 in words is "twenty-one million, six hundred eighty-five thousand, six hundred eighty".