21720607 has 4 divisors (see below), whose sum is σ = 21810976. Its totient is φ = 21630240.

The previous prime is 21720599. The next prime is 21720613. The reversal of 21720607 is 70602712.

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 21720607 - 2³ = 21720599 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 (21720617) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 44823 + ... + 45304.

It is an arithmetic number, because the mean of its divisors is an integer number (5452744).

Almost surely, 2^21720607 is an apocalyptic number.

21720607 is a deficient number, since it is larger than the sum of its proper divisors (90369).

21720607 is an equidigital number, since it uses as much as digits as its factorization.

21720607 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90368.

The product of its (nonzero) digits is 1176, while the sum is 25.

The square root of 21720607 is about 4660.5372007956. The cubic root of 21720607 is about 279.0127090899.

The spelling of 21720607 in words is "twenty-one million, seven hundred twenty thousand, six hundred seven".