21317911 has 4 divisors (see below), whose sum is σ = 21350824. Its totient is φ = 21285000.

The previous prime is 21317899. The next prime is 21317921. The reversal of 21317911 is 11971312.

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 21317911 - 2¹⁷ = 21186839 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 (21317921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15465 + ... + 16786.

It is an arithmetic number, because the mean of its divisors is an integer number (5337706).

Almost surely, 2^21317911 is an apocalyptic number.

21317911 is a deficient number, since it is larger than the sum of its proper divisors (32913).

21317911 is an equidigital number, since it uses as much as digits as its factorization.

21317911 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32912.

The product of its digits is 378, while the sum is 25.

The square root of 21317911 is about 4617.1323351188. The cubic root of 21317911 is about 277.2776608245.

The spelling of 21317911 in words is "twenty-one million, three hundred seventeen thousand, nine hundred eleven".