204155561 has 4 divisors (see below), whose sum is σ = 205047300. Its totient is φ = 203263824.

The previous prime is 204155537. The next prime is 204155569. The reversal of 204155561 is 165551402.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 165551402 = 2 ⋅82775701.

It can be written as a sum of positive squares in 2 ways, for example, as 112360000 + 91795561 = 10600^2 + 9581^2 .

It is a cyclic number.

It is not a de Polignac number, because 204155561 - 2¹⁰ = 204154537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (204155569) 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 in 3 ways as a sum of consecutive naturals, for example, 445526 + ... + 445983.

It is an arithmetic number, because the mean of its divisors is an integer number (51261825).

Almost surely, 2^204155561 is an apocalyptic number.

It is an amenable number.

204155561 is a deficient number, since it is larger than the sum of its proper divisors (891739).

204155561 is an equidigital number, since it uses as much as digits as its factorization.

204155561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 891738.

The product of its (nonzero) digits is 6000, while the sum is 29.

The square root of 204155561 is about 14288.3015435705. The cubic root of 204155561 is about 588.8261262027.

The spelling of 204155561 in words is "two hundred four million, one hundred fifty-five thousand, five hundred sixty-one".