21969209 has 4 divisors (see below), whose sum is σ = 22924416. Its totient is φ = 21014004.

The previous prime is 21969203. The next prime is 21969221. The reversal of 21969209 is 90296912.

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 21969209 - 2⁴ = 21969193 is a prime.

It is a super-2 number, since 2×21969209² = 965292288171362, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21969203) 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, 477569 + ... + 477614.

It is an arithmetic number, because the mean of its divisors is an integer number (5731104).

Almost surely, 2^21969209 is an apocalyptic number.

It is an amenable number.

21969209 is a deficient number, since it is larger than the sum of its proper divisors (955207).

21969209 is an equidigital number, since it uses as much as digits as its factorization.

21969209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 955206.

The product of its (nonzero) digits is 17496, while the sum is 38.

The square root of 21969209 is about 4687.1322789100. The cubic root of 21969209 is about 280.0731484057.

The spelling of 21969209 in words is "twenty-one million, nine hundred sixty-nine thousand, two hundred nine".