206209921 has 4 divisors (see below), whose sum is σ = 206651952. Its totient is φ = 205767892.

The previous prime is 206209901. The next prime is 206209933. The reversal of 206209921 is 129902602.

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, and also an emirpimes, since its reverse is a distinct semiprime: 129902602 = 2 ⋅64951301.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-206209921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (206209901) 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, 220315 + ... + 221248.

It is an arithmetic number, because the mean of its divisors is an integer number (51662988).

Almost surely, 2^206209921 is an apocalyptic number.

It is an amenable number.

206209921 is a deficient number, since it is larger than the sum of its proper divisors (442031).

206209921 is an equidigital number, since it uses as much as digits as its factorization.

206209921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 442030.

The product of its (nonzero) digits is 3888, while the sum is 31.

The square root of 206209921 is about 14360.0111768759. The cubic root of 206209921 is about 590.7946020623.

The spelling of 206209921 in words is "two hundred six million, two hundred nine thousand, nine hundred twenty-one".