209642921 has 2 divisors, whose sum is σ = 209642922. Its totient is φ = 209642920.

The previous prime is 209642893. The next prime is 209643013. The reversal of 209642921 is 129246902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 115261696 + 94381225 = 10736^2 + 9715^2 .

It is a cyclic number.

It is not a de Polignac number, because 209642921 - 2⁶ = 209642857 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (209642821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104821460 + 104821461.

It is an arithmetic number, because the mean of its divisors is an integer number (104821461).

Almost surely, 2^209642921 is an apocalyptic number.

It is an amenable number.

209642921 is a deficient number, since it is larger than the sum of its proper divisors (1).

209642921 is an equidigital number, since it uses as much as digits as its factorization.

209642921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 15552, while the sum is 35.

The square root of 209642921 is about 14479.0511084118. The cubic root of 209642921 is about 594.0551073664.

The spelling of 209642921 in words is "two hundred nine million, six hundred forty-two thousand, nine hundred twenty-one".