21005717 has 8 divisors (see below), whose sum is σ = 21415680. Its totient is φ = 20599920.

The previous prime is 21005713. The next prime is 21005737. The reversal of 21005717 is 71750012.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21005717 - 2² = 21005713 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21005692 and 21005701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005713) 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, 10292 + ... + 12162.

It is an arithmetic number, because the mean of its divisors is an integer number (2676960).

Almost surely, 2^21005717 is an apocalyptic number.

It is an amenable number.

21005717 is a deficient number, since it is larger than the sum of its proper divisors (409963).

21005717 is a wasteful number, since it uses less digits than its factorization.

21005717 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2083.

The product of its (nonzero) digits is 490, while the sum is 23.

The square root of 21005717 is about 4583.1994283470. The cubic root of 21005717 is about 275.9174515086.

Adding to 21005717 its reverse (71750012), we get a palindrome (92755729).

The spelling of 21005717 in words is "twenty-one million, five thousand, seven hundred seventeen".