1661204761 has 4 divisors (see below), whose sum is σ = 1661353524. Its totient is φ = 1661056000.

The previous prime is 1661204731. The next prime is 1661204771. The reversal of 1661204761 is 1674021661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1674021661 = 13 ⋅128770897.

It can be written as a sum of positive squares in 2 ways, for example, as 441798361 + 1219406400 = 21019^2 + 34920^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661204761 - 2²¹ = 1659107609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1661204731) 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, 56140 + ... + 80461.

It is an arithmetic number, because the mean of its divisors is an integer number (415338381).

Almost surely, 2^1661204761 is an apocalyptic number.

It is an amenable number.

1661204761 is a deficient number, since it is larger than the sum of its proper divisors (148763).

1661204761 is a wasteful number, since it uses less digits than its factorization.

1661204761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 148762.

The product of its (nonzero) digits is 12096, while the sum is 34.

The square root of 1661204761 is about 40757.8797412230. The cubic root of 1661204761 is about 1184.3345230593.

The spelling of 1661204761 in words is "one billion, six hundred sixty-one million, two hundred four thousand, seven hundred sixty-one".