21720767 has 4 divisors (see below), whose sum is σ = 21735936. Its totient is φ = 21705600.

The previous prime is 21720749. The next prime is 21720779. The reversal of 21720767 is 76702712.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21720767 - 2⁶ = 21720703 is a prime.

It is a Duffinian number.

It is a congruent number.

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

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5183 + ... + 8384.

It is an arithmetic number, because the mean of its divisors is an integer number (5433984).

Almost surely, 2^21720767 is an apocalyptic number.

21720767 is a deficient number, since it is larger than the sum of its proper divisors (15169).

21720767 is a wasteful number, since it uses less digits than its factorization.

21720767 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15168.

The product of its (nonzero) digits is 8232, while the sum is 32.

The square root of 21720767 is about 4660.5543661672. The cubic root of 21720767 is about 279.0133941832.

The spelling of 21720767 in words is "twenty-one million, seven hundred twenty thousand, seven hundred sixty-seven".