1561365891 has 6 divisors (see below), whose sum is σ = 2255306300. Its totient is φ = 1040910588.

The previous prime is 1561365889. The next prime is 1561365913. The reversal of 1561365891 is 1985631651.

1561365891 is a `hidden beast` number, since 1 + 5 + 61 + 3 + 6 + 589 + 1 = 666.

It is not a de Polignac number, because 1561365891 - 2¹ = 1561365889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1561365791) 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 5 ways as a sum of consecutive naturals, for example, 86742541 + ... + 86742558.

Almost surely, 2^1561365891 is an apocalyptic number.

1561365891 is a deficient number, since it is larger than the sum of its proper divisors (693940409).

1561365891 is a wasteful number, since it uses less digits than its factorization.

1561365891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 173485105 (or 173485102 counting only the distinct ones).

The product of its digits is 194400, while the sum is 45.

The square root of 1561365891 is about 39514.1226778477. The cubic root of 1561365891 is about 1160.1163901744.

The spelling of 1561365891 in words is "one billion, five hundred sixty-one million, three hundred sixty-five thousand, eight hundred ninety-one".