1561760821 has 4 divisors (see below), whose sum is σ = 1585070752. Its totient is φ = 1538450892.

The previous prime is 1561760773. The next prime is 1561760831. The reversal of 1561760821 is 1280671651.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1561760821 - 2¹¹ = 1561758773 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 (1561760831) 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, 11654865 + ... + 11654998.

It is an arithmetic number, because the mean of its divisors is an integer number (396267688).

Almost surely, 2^1561760821 is an apocalyptic number.

It is an amenable number.

1561760821 is a deficient number, since it is larger than the sum of its proper divisors (23309931).

1561760821 is an equidigital number, since it uses as much as digits as its factorization.

1561760821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23309930.

The product of its (nonzero) digits is 20160, while the sum is 37.

The square root of 1561760821 is about 39519.1196890821. The cubic root of 1561760821 is about 1160.2141947409.

The spelling of 1561760821 in words is "one billion, five hundred sixty-one million, seven hundred sixty thousand, eight hundred twenty-one".