21566880 has 144 divisors (see below), whose sum is σ = 78014664. Its totient is φ = 5406720.

The previous prime is 21566873. The next prime is 21566887. The reversal of 21566880 is 8866512.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21566873) and next prime (21566887).

It can be written as a sum of positive squares in 4 ways, for example, as 16744464 + 4822416 = 4092^2 + 2196^2 .

It is a tau number, because it is divible by the number of its divisors (144).

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 (21566887) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 24040 + ... + 24920.

Almost surely, 2^21566880 is an apocalyptic number.

21566880 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 21566880, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39007332).

21566880 is an abundant number, since it is smaller than the sum of its proper divisors (56447784).

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

21566880 is a wasteful number, since it uses less digits than its factorization.

21566880 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 919 (or 908 counting only the distinct ones).

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

The square root of 21566880 is about 4644.0155038501. The cubic root of 21566880 is about 278.3529151446.

The spelling of 21566880 in words is "twenty-one million, five hundred sixty-six thousand, eight hundred eighty".