21718517 has 4 divisors (see below), whose sum is σ = 21848736. Its totient is φ = 21588300.

The previous prime is 21718513. The next prime is 21718523. The reversal of 21718517 is 71581712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21718517 - 2² = 21718513 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 (21718513) 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, 64859 + ... + 65192.

It is an arithmetic number, because the mean of its divisors is an integer number (5462184).

Almost surely, 2^21718517 is an apocalyptic number.

It is an amenable number.

21718517 is a deficient number, since it is larger than the sum of its proper divisors (130219).

21718517 is a wasteful number, since it uses less digits than its factorization.

21718517 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 130218.

The product of its digits is 3920, while the sum is 32.

The square root of 21718517 is about 4660.3129723228. The cubic root of 21718517 is about 279.0037597503.

The spelling of 21718517 in words is "twenty-one million, seven hundred eighteen thousand, five hundred seventeen".