21718729 has 4 divisors (see below), whose sum is σ = 22861840. Its totient is φ = 20575620.

The previous prime is 21718721. The next prime is 21718751. The reversal of 21718729 is 92781712.

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 21718729 - 2³ = 21718721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21718721) 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, 571527 + ... + 571564.

It is an arithmetic number, because the mean of its divisors is an integer number (5715460).

Almost surely, 2^21718729 is an apocalyptic number.

It is an amenable number.

21718729 is a deficient number, since it is larger than the sum of its proper divisors (1143111).

21718729 is a wasteful number, since it uses less digits than its factorization.

21718729 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1143110.

The product of its digits is 14112, while the sum is 37.

The square root of 21718729 is about 4660.3357175208. The cubic root of 21718729 is about 279.0046675564.

The spelling of 21718729 in words is "twenty-one million, seven hundred eighteen thousand, seven hundred twenty-nine".