21711209 has 4 divisors (see below), whose sum is σ = 23381316. Its totient is φ = 20041104.

The previous prime is 21711163. The next prime is 21711229. The reversal of 21711209 is 90211712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12390400 + 9320809 = 3520^2 + 3053^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21711209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21711229) 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, 835034 + ... + 835059.

It is an arithmetic number, because the mean of its divisors is an integer number (5845329).

Almost surely, 2^21711209 is an apocalyptic number.

It is an amenable number.

21711209 is a deficient number, since it is larger than the sum of its proper divisors (1670107).

21711209 is a wasteful number, since it uses less digits than its factorization.

21711209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1670106.

The product of its (nonzero) digits is 252, while the sum is 23.

The square root of 21711209 is about 4659.5288388420. The cubic root of 21711209 is about 278.9724625211.

The spelling of 21711209 in words is "twenty-one million, seven hundred eleven thousand, two hundred nine".