205121643 has 16 divisors (see below), whose sum is σ = 289941120. Its totient is φ = 128544896.

The previous prime is 205121641. The next prime is 205121681. The reversal of 205121643 is 346121502.

It is a cyclic number.

It is not a de Polignac number, because 205121643 - 2¹ = 205121641 is a prime.

It is not an unprimeable number, because it can be changed into a prime (205121641) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 49996 + ... + 53942.

It is an arithmetic number, because the mean of its divisors is an integer number (18121320).

Almost surely, 2^205121643 is an apocalyptic number.

205121643 is a deficient number, since it is larger than the sum of its proper divisors (84819477).

205121643 is a wasteful number, since it uses less digits than its factorization.

205121643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4986.

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 205121643 is about 14322.0683911228. The cubic root of 205121643 is about 589.7534572714.

It can be divided in two parts, 20512 and 1643, that added together give a triangular number (22155 = T₂₁₀).

The spelling of 205121643 in words is "two hundred five million, one hundred twenty-one thousand, six hundred forty-three".