204721661 has 4 divisors (see below), whose sum is σ = 204774300. Its totient is φ = 204669024.

The previous prime is 204721609. The next prime is 204721663. The reversal of 204721661 is 166127402.

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 204318436 + 403225 = 14294^2 + 635^2 .

It is a cyclic number.

It is not a de Polignac number, because 204721661 - 2²² = 200527357 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (204721663) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 19976 + ... + 28433.

It is an arithmetic number, because the mean of its divisors is an integer number (51193575).

Almost surely, 2^204721661 is an apocalyptic number.

It is an amenable number.

204721661 is a deficient number, since it is larger than the sum of its proper divisors (52639).

204721661 is an equidigital number, since it uses as much as digits as its factorization.

204721661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 52638.

The product of its (nonzero) digits is 4032, while the sum is 29.

The square root of 204721661 is about 14308.0977421878. The cubic root of 204721661 is about 589.3698730768.

The spelling of 204721661 in words is "two hundred four million, seven hundred twenty-one thousand, six hundred sixty-one".