205890721 has 4 divisors (see below), whose sum is σ = 205959492. Its totient is φ = 205821952.

The previous prime is 205890709. The next prime is 205890761. The reversal of 205890721 is 127098502.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 189447696 + 16443025 = 13764^2 + 4055^2 .

It is a cyclic number.

It is not a de Polignac number, because 205890721 - 2²³ = 197502113 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (205890761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 29680 + ... + 35953.

It is an arithmetic number, because the mean of its divisors is an integer number (51489873).

Almost surely, 2^205890721 is an apocalyptic number.

It is an amenable number.

205890721 is a deficient number, since it is larger than the sum of its proper divisors (68771).

205890721 is an equidigital number, since it uses as much as digits as its factorization.

205890721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 68770.

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 205890721 is about 14348.8926750464. The cubic root of 205890721 is about 590.4896069971.

The spelling of 205890721 in words is "two hundred five million, eight hundred ninety thousand, seven hundred twenty-one".