1561547561 has 4 divisors (see below), whose sum is σ = 1784625792. Its totient is φ = 1338469332.

The previous prime is 1561547551. The next prime is 1561547569. The reversal of 1561547561 is 1657451651.

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 a de Polignac number, because none of the positive numbers 2^k-1561547561 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1561547569) 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, 111539105 + ... + 111539118.

It is an arithmetic number, because the mean of its divisors is an integer number (446156448).

Almost surely, 2^1561547561 is an apocalyptic number.

It is an amenable number.

1561547561 is a deficient number, since it is larger than the sum of its proper divisors (223078231).

1561547561 is an equidigital number, since it uses as much as digits as its factorization.

1561547561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 223078230.

The product of its digits is 126000, while the sum is 41.

The square root of 1561547561 is about 39516.4214093331. The cubic root of 1561547561 is about 1160.1613828679.

The spelling of 1561547561 in words is "one billion, five hundred sixty-one million, five hundred forty-seven thousand, five hundred sixty-one".