209812321 has 2 divisors, whose sum is σ = 209812322. Its totient is φ = 209812320.

The previous prime is 209812301. The next prime is 209812327. The reversal of 209812321 is 123218902.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 125888400 + 83923921 = 11220^2 + 9161^2 .

It is a cyclic number.

It is not a de Polignac number, because 209812321 - 2⁹ = 209811809 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 209812321.

It is not a weakly prime, because it can be changed into another prime (209812327) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104906160 + 104906161.

It is an arithmetic number, because the mean of its divisors is an integer number (104906161).

Almost surely, 2^209812321 is an apocalyptic number.

It is an amenable number.

209812321 is a deficient number, since it is larger than the sum of its proper divisors (1).

209812321 is an equidigital number, since it uses as much as digits as its factorization.

209812321 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1728, while the sum is 28.

The square root of 209812321 is about 14484.8997580239. The cubic root of 209812321 is about 594.2150711781.

The spelling of 209812321 in words is "two hundred nine million, eight hundred twelve thousand, three hundred twenty-one".