21720687 has 8 divisors (see below), whose sum is σ = 29022336. Its totient is φ = 14449752.

The previous prime is 21720649. The next prime is 21720689. The reversal of 21720687 is 78602712.

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

It is not a de Polignac number, because 21720687 - 2⁸ = 21720431 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720689) 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, 5973 + ... + 8894.

It is an arithmetic number, because the mean of its divisors is an integer number (3627792).

Almost surely, 2^21720687 is an apocalyptic number.

21720687 is a deficient number, since it is larger than the sum of its proper divisors (7301649).

21720687 is a wasteful number, since it uses less digits than its factorization.

21720687 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15357.

The product of its (nonzero) digits is 9408, while the sum is 33.

The square root of 21720687 is about 4660.5457834893. The cubic root of 21720687 is about 279.0130516370.

The spelling of 21720687 in words is "twenty-one million, seven hundred twenty thousand, six hundred eighty-seven".