21765680 has 40 divisors (see below), whose sum is σ = 51312192. Its totient is φ = 8584704.

The previous prime is 21765647. The next prime is 21765683. The reversal of 21765680 is 8656712.

It is a tau number, because it is divible by the number of its divisors (40).

It is a self number, because there is not a number n which added to its sum of digits gives 21765680.

It is not an unprimeable number, because it can be changed into a prime (21765683) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3977 + ... + 7703.

Almost surely, 2^21765680 is an apocalyptic number.

21765680 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 21765680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25656096).

21765680 is an abundant number, since it is smaller than the sum of its proper divisors (29546512).

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

21765680 is a wasteful number, since it uses less digits than its factorization.

21765680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3813 (or 3807 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 35.

The square root of 21765680 is about 4665.3702961287. The cubic root of 21765680 is about 279.2055712717.

The spelling of 21765680 in words is "twenty-one million, seven hundred sixty-five thousand, six hundred eighty".