21685764 has 48 divisors (see below), whose sum is σ = 53625600. Its totient is φ = 6801696.

The previous prime is 21685751. The next prime is 21685787. The reversal of 21685764 is 46758612.

Its product of digits (80640) is a multiple of the sum of its prime factors (672).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 51547 + ... + 51965.

It is an arithmetic number, because the mean of its divisors is an integer number (1117200).

Almost surely, 2^21685764 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 21685764, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26812800).

21685764 is an abundant number, since it is smaller than the sum of its proper divisors (31939836).

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

21685764 is a wasteful number, since it uses less digits than its factorization.

21685764 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 672 (or 670 counting only the distinct ones).

The product of its digits is 80640, while the sum is 39.

The square root of 21685764 is about 4656.7976120935. The cubic root of 21685764 is about 278.8634369760.

The spelling of 21685764 in words is "twenty-one million, six hundred eighty-five thousand, seven hundred sixty-four".