161555561 has 4 divisors (see below), whose sum is σ = 161812224. Its totient is φ = 161298900.

The previous prime is 161555551. The next prime is 161555567. The reversal of 161555561 is 165555161.

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 161555561 - 2¹⁰ = 161554537 is a prime.

It is a super-2 number, since 2×161555561² = 52200398580049442, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (161555567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 127385 + ... + 128646.

It is an arithmetic number, because the mean of its divisors is an integer number (40453056).

Almost surely, 2^161555561 is an apocalyptic number.

It is an amenable number.

161555561 is a deficient number, since it is larger than the sum of its proper divisors (256663).

161555561 is an equidigital number, since it uses as much as digits as its factorization.

161555561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 256662.

The product of its digits is 22500, while the sum is 35.

The square root of 161555561 is about 12710.4508574637. The cubic root of 161555561 is about 544.6372032058.

The spelling of 161555561 in words is "one hundred sixty-one million, five hundred fifty-five thousand, five hundred sixty-one".