21009311 has 4 divisors (see below), whose sum is σ = 21733800. Its totient is φ = 20284824.

The previous prime is 21009283. The next prime is 21009337. The reversal of 21009311 is 11390012.

It is a happy number.

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 21009311 - 2¹⁰ = 21008287 is a prime.

It is a super-2 number, since 2×21009311² = 882782297389442, which contains 22 as substring.

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 21009311.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21009211) 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, 362201 + ... + 362258.

It is an arithmetic number, because the mean of its divisors is an integer number (5433450).

Almost surely, 2^21009311 is an apocalyptic number.

21009311 is a deficient number, since it is larger than the sum of its proper divisors (724489).

21009311 is an equidigital number, since it uses as much as digits as its factorization.

21009311 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 724488.

The product of its (nonzero) digits is 54, while the sum is 17.

The square root of 21009311 is about 4583.5914957596. The cubic root of 21009311 is about 275.9331867609.

Adding to 21009311 its reverse (11390012), we get a palindrome (32399323).

It can be divided in two parts, 2100 and 9311, that added together give a palindrome (11411).

The spelling of 21009311 in words is "twenty-one million, nine thousand, three hundred eleven".