21720787 has 8 divisors (see below), whose sum is σ = 23792832. Its totient is φ = 19665000.

The previous prime is 21720779. The next prime is 21720821. The reversal of 21720787 is 78702712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21720787 - 2³ = 21720779 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21720707) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1173 + ... + 6694.

It is an arithmetic number, because the mean of its divisors is an integer number (2974104).

Almost surely, 2^21720787 is an apocalyptic number.

21720787 is a deficient number, since it is larger than the sum of its proper divisors (2072045).

21720787 is a wasteful number, since it uses less digits than its factorization.

21720787 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8129.

The product of its (nonzero) digits is 10976, while the sum is 34.

The square root of 21720787 is about 4660.5565118342. The cubic root of 21720787 is about 279.0134798196.

The spelling of 21720787 in words is "twenty-one million, seven hundred twenty thousand, seven hundred eighty-seven".