21720660 has 48 divisors (see below), whose sum is σ = 65498496. Its totient is φ = 5346432.

The previous prime is 21720649. The next prime is 21720689. The reversal of 21720660 is 6602712.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21720660.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13144 + ... + 14703.

It is an arithmetic number, because the mean of its divisors is an integer number (1364552).

Almost surely, 2^21720660 is an apocalyptic number.

21720660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21720660 is an abundant number, since it is smaller than the sum of its proper divisors (43777836).

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

21720660 is a wasteful number, since it uses less digits than its factorization.

21720660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27872 (or 27870 counting only the distinct ones).

The product of its (nonzero) digits is 1008, while the sum is 24.

The square root of 21720660 is about 4660.5428868320. The cubic root of 21720660 is about 279.0129360274.

The spelling of 21720660 in words is "twenty-one million, seven hundred twenty thousand, six hundred sixty".