21680780 has 108 divisors (see below), whose sum is σ = 54876864. Its totient is φ = 7180800.

The previous prime is 21680741. The next prime is 21680783. The reversal of 21680780 is 8708612.

It is not an unprimeable number, because it can be changed into a prime (21680783) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 699365 + ... + 699395.

Almost surely, 2^21680780 is an apocalyptic number.

21680780 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 21680780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27438432).

21680780 is an abundant number, since it is smaller than the sum of its proper divisors (33196084).

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

21680780 is a wasteful number, since it uses less digits than its factorization.

21680780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 96 (or 66 counting only the distinct ones).

The product of its (nonzero) digits is 5376, while the sum is 32.

The square root of 21680780 is about 4656.2624496478. The cubic root of 21680780 is about 278.8420717790.

The spelling of 21680780 in words is "twenty-one million, six hundred eighty thousand, seven hundred eighty".