21680820 has 72 divisors (see below), whose sum is σ = 75164544. Its totient is φ = 4955328.

The previous prime is 21680819. The next prime is 21680833. The reversal of 21680820 is 2808612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7344 + ... + 9863.

It is an arithmetic number, because the mean of its divisors is an integer number (1043952).

Almost surely, 2^21680820 is an apocalyptic number.

21680820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21680820 is an abundant number, since it is smaller than the sum of its proper divisors (53483724).

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

21680820 is a wasteful number, since it uses less digits than its factorization.

21680820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17229 (or 17224 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 27.

The square root of 21680820 is about 4656.2667449363. The cubic root of 21680820 is about 278.8422432623.

It can be divided in two parts, 21680 and 820, that added together give a square (22500 = 150²).

The spelling of 21680820 in words is "twenty-one million, six hundred eighty thousand, eight hundred twenty".