21271209 has 4 divisors (see below), whose sum is σ = 28361616. Its totient is φ = 14180804.

The previous prime is 21271207. The next prime is 21271223. The reversal of 21271209 is 90217212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21271209 - 2¹ = 21271207 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21271207) 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, 3545199 + ... + 3545204.

It is an arithmetic number, because the mean of its divisors is an integer number (7090404).

Almost surely, 2^21271209 is an apocalyptic number.

It is an amenable number.

21271209 is a deficient number, since it is larger than the sum of its proper divisors (7090407).

21271209 is an equidigital number, since it uses as much as digits as its factorization.

21271209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7090406.

The product of its (nonzero) digits is 504, while the sum is 24.

The square root of 21271209 is about 4612.0720939725. The cubic root of 21271209 is about 277.0750316971.

The spelling of 21271209 in words is "twenty-one million, two hundred seventy-one thousand, two hundred nine".