21680720 has 40 divisors (see below), whose sum is σ = 52603776. Its totient is φ = 8294528.

The previous prime is 21680717. The next prime is 21680741. The reversal of 21680720 is 2708612.

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 21680720.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4052 + ... + 7731.

Almost surely, 2^21680720 is an apocalyptic number.

21680720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21680720 is an abundant number, since it is smaller than the sum of its proper divisors (30923056).

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

21680720 is a wasteful number, since it uses less digits than its factorization.

21680720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11819 (or 11813 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 26.

The square root of 21680720 is about 4656.2560067075. The cubic root of 21680720 is about 278.8418145537.

The spelling of 21680720 in words is "twenty-one million, six hundred eighty thousand, seven hundred twenty".