209168821 has 2 divisors, whose sum is σ = 209168822. Its totient is φ = 209168820.

The previous prime is 209168819. The next prime is 209168863. The reversal of 209168821 is 128861902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 151560721 + 57608100 = 12311^2 + 7590^2 .

It is a cyclic number.

It is not a de Polignac number, because 209168821 - 2¹ = 209168819 is a prime.

Together with 209168819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (209168621) 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, 104584410 + 104584411.

It is an arithmetic number, because the mean of its divisors is an integer number (104584411).

Almost surely, 2^209168821 is an apocalyptic number.

It is an amenable number.

209168821 is a deficient number, since it is larger than the sum of its proper divisors (1).

209168821 is an equidigital number, since it uses as much as digits as its factorization.

209168821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 13824, while the sum is 37.

The square root of 209168821 is about 14462.6699125715. The cubic root of 209168821 is about 593.6069578819.

The spelling of 209168821 in words is "two hundred nine million, one hundred sixty-eight thousand, eight hundred twenty-one".