21767680 has 80 divisors (see below), whose sum is σ = 57009744. Its totient is φ = 7905280.

The previous prime is 21767659. The next prime is 21767687. The reversal of 21767680 is 8676712.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (80).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21767687) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 27774 + ... + 28546.

Almost surely, 2^21767680 is an apocalyptic number.

21767680 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 21767680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28504872).

21767680 is an abundant number, since it is smaller than the sum of its proper divisors (35242064).

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

21767680 is an equidigital number, since it uses as much as digits as its factorization.

21767680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 807 (or 791 counting only the distinct ones).

The product of its (nonzero) digits is 28224, while the sum is 37.

The square root of 21767680 is about 4665.5846364630. The cubic root of 21767680 is about 279.2141228697.

The spelling of 21767680 in words is "twenty-one million, seven hundred sixty-seven thousand, six hundred eighty".