166851561 has 4 divisors (see below), whose sum is σ = 222468752. Its totient is φ = 111234372.

The previous prime is 166851539. The next prime is 166851563. The reversal of 166851561 is 165158661.

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: 165158661 = 3 ⋅55052887.

It is not a de Polignac number, because 166851561 - 2¹⁸ = 166589417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (166851563) 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, 27808591 + ... + 27808596.

It is an arithmetic number, because the mean of its divisors is an integer number (55617188).

Almost surely, 2^166851561 is an apocalyptic number.

It is an amenable number.

166851561 is a deficient number, since it is larger than the sum of its proper divisors (55617191).

166851561 is an equidigital number, since it uses as much as digits as its factorization.

166851561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55617190.

The product of its digits is 43200, while the sum is 39.

The square root of 166851561 is about 12917.1034291748. The cubic root of 166851561 is about 550.5246354883.

The spelling of 166851561 in words is "one hundred sixty-six million, eight hundred fifty-one thousand, five hundred sixty-one".