21005711 has 8 divisors (see below), whose sum is σ = 21436800. Its totient is φ = 20577240.

The previous prime is 21005707. The next prime is 21005713. The reversal of 21005711 is 11750012.

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 21005711 - 2² = 21005707 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21005711.

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, 25496 + ... + 26306.

It is an arithmetic number, because the mean of its divisors is an integer number (2679600).

Almost surely, 2^21005711 is an apocalyptic number.

21005711 is a deficient number, since it is larger than the sum of its proper divisors (431089).

21005711 is an equidigital number, since it uses as much as digits as its factorization.

21005711 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1309.

The product of its (nonzero) digits is 70, while the sum is 17.

The square root of 21005711 is about 4583.1987737823. The cubic root of 21005711 is about 275.9174252379.

Adding to 21005711 its reverse (11750012), we get a palindrome (32755723).

The spelling of 21005711 in words is "twenty-one million, five thousand, seven hundred eleven".