205421309 has 2 divisors, whose sum is σ = 205421310. Its totient is φ = 205421308.

The previous prime is 205421273. The next prime is 205421311. The reversal of 205421309 is 903124502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 114276100 + 91145209 = 10690^2 + 9547^2 .

It is a cyclic number.

It is not a de Polignac number, because 205421309 - 2⁸ = 205421053 is a prime.

Together with 205421311, it forms a pair of twin primes.

It is a Chen prime.

It is equal to p_11362436 and since 205421309 and 11362436 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (205421329) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 102710654 + 102710655.

It is an arithmetic number, because the mean of its divisors is an integer number (102710655).

Almost surely, 2^205421309 is an apocalyptic number.

It is an amenable number.

205421309 is a deficient number, since it is larger than the sum of its proper divisors (1).

205421309 is an equidigital number, since it uses as much as digits as its factorization.

205421309 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2160, while the sum is 26.

The square root of 205421309 is about 14332.5262602236. The cubic root of 205421309 is about 590.0405114383.

The spelling of 205421309 in words is "two hundred five million, four hundred twenty-one thousand, three hundred nine".