21057680 has 80 divisors (see below), whose sum is σ = 57805824. Its totient is φ = 6981120.

The previous prime is 21057671. The next prime is 21057691. The reversal of 21057680 is 8675012.

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

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 16754 + ... + 17966.

Almost surely, 2^21057680 is an apocalyptic number.

21057680 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 21057680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28902912).

21057680 is an abundant number, since it is smaller than the sum of its proper divisors (36748144).

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

21057680 is a wasteful number, since it uses less digits than its factorization.

21057680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1264 (or 1258 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 29.

The square root of 21057680 is about 4588.8647833642. The cubic root of 21057680 is about 276.1447815615.

The spelling of 21057680 in words is "twenty-one million, fifty-seven thousand, six hundred eighty".