21718691 has 4 divisors (see below), whose sum is σ = 22861800. Its totient is φ = 20575584.

The previous prime is 21718681. The next prime is 21718703. The reversal of 21718691 is 19681712.

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 21718691 - 2¹⁰ = 21717667 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21718681) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 571526 + ... + 571563.

It is an arithmetic number, because the mean of its divisors is an integer number (5715450).

Almost surely, 2^21718691 is an apocalyptic number.

21718691 is a deficient number, since it is larger than the sum of its proper divisors (1143109).

21718691 is a wasteful number, since it uses less digits than its factorization.

21718691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1143108.

The product of its digits is 6048, while the sum is 35.

The square root of 21718691 is about 4660.3316405595. The cubic root of 21718691 is about 279.0045048368.

The spelling of 21718691 in words is "twenty-one million, seven hundred eighteen thousand, six hundred ninety-one".