161566561 has 4 divisors (see below), whose sum is σ = 173994772. Its totient is φ = 149138352.

The previous prime is 161566553. The next prime is 161566577. The reversal of 161566561 is 165665161.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 165665161 = 19 ⋅8719219.

It can be written as a sum of positive squares in 2 ways, for example, as 95648400 + 65918161 = 9780^2 + 8119^2 .

It is a cyclic number.

It is not a de Polignac number, because 161566561 - 2³ = 161566553 is a prime.

It is a super-2 number, since 2×161566561² = 52207507266733442, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 161566561.

It is not an unprimeable number, because it can be changed into a prime (161566591) 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 3 ways as a sum of consecutive naturals, for example, 6214086 + ... + 6214111.

It is an arithmetic number, because the mean of its divisors is an integer number (43498693).

Almost surely, 2^161566561 is an apocalyptic number.

It is an amenable number.

161566561 is a deficient number, since it is larger than the sum of its proper divisors (12428211).

161566561 is a wasteful number, since it uses less digits than its factorization.

161566561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12428210.

The product of its digits is 32400, while the sum is 37.

The square root of 161566561 is about 12710.8835648825. The cubic root of 161566561 is about 544.6495640168.

The spelling of 161566561 in words is "one hundred sixty-one million, five hundred sixty-six thousand, five hundred sixty-one".