161509861 has 4 divisors (see below), whose sum is σ = 170010400. Its totient is φ = 153009324.

The previous prime is 161509853. The next prime is 161509879. The reversal of 161509861 is 168905161.

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, and also an emirpimes, since its reverse is a distinct semiprime: 168905161 = 43 ⋅3928027.

It is a cyclic number.

It is not a de Polignac number, because 161509861 - 2³ = 161509853 is a prime.

It is a super-3 number, since 3×161509861³ (a number of 26 digits) contains 333 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 161509861.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161509561) 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, 4250241 + ... + 4250278.

It is an arithmetic number, because the mean of its divisors is an integer number (42502600).

Almost surely, 2^161509861 is an apocalyptic number.

It is an amenable number.

161509861 is a deficient number, since it is larger than the sum of its proper divisors (8500539).

161509861 is an equidigital number, since it uses as much as digits as its factorization.

161509861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8500538.

The product of its (nonzero) digits is 12960, while the sum is 37.

The square root of 161509861 is about 12708.6529970725. The cubic root of 161509861 is about 544.5858436460.

The spelling of 161509861 in words is "one hundred sixty-one million, five hundred nine thousand, eight hundred sixty-one".