165601555561 has 4 divisors (see below), whose sum is σ = 178340136772. Its totient is φ = 152862974352.

The previous prime is 165601555547. The next prime is 165601555573. The reversal of 165601555561 is 165555106561.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 75745497961 + 89856057600 = 275219^2 + 299760^2 .

It is a cyclic number.

It is not a de Polignac number, because 165601555561 - 2⁷ = 165601555433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165601555261) 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, 6369290586 + ... + 6369290611.

It is an arithmetic number, because the mean of its divisors is an integer number (44585034193).

Almost surely, 2^165601555561 is an apocalyptic number.

It is an amenable number.

165601555561 is a deficient number, since it is larger than the sum of its proper divisors (12738581211).

165601555561 is a wasteful number, since it uses less digits than its factorization.

165601555561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12738581210.

The product of its (nonzero) digits is 675000, while the sum is 46.

The spelling of 165601555561 in words is "one hundred sixty-five billion, six hundred one million, five hundred fifty-five thousand, five hundred sixty-one".