209618921 has 2 divisors, whose sum is σ = 209618922. Its totient is φ = 209618920.

The previous prime is 209618897. The next prime is 209618933. The reversal of 209618921 is 129816902.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 193905625 + 15713296 = 13925^2 + 3964^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-209618921 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 (209618951) 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, 104809460 + 104809461.

It is an arithmetic number, because the mean of its divisors is an integer number (104809461).

Almost surely, 2^209618921 is an apocalyptic number.

It is an amenable number.

209618921 is a deficient number, since it is larger than the sum of its proper divisors (1).

209618921 is an equidigital number, since it uses as much as digits as its factorization.

209618921 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 38.

The square root of 209618921 is about 14478.2223010976. Note that the first 3 decimals coincide. The cubic root of 209618921 is about 594.0324372844.

The spelling of 209618921 in words is "two hundred nine million, six hundred eighteen thousand, nine hundred twenty-one".