166561791 has 32 divisors (see below), whose sum is σ = 260997120. Its totient is φ = 93429600.

The previous prime is 166561763. The next prime is 166561793. The reversal of 166561791 is 197165661.

It is not a de Polignac number, because 166561791 - 2¹⁹ = 166037503 is a prime.

It is a super-2 number, since 2×166561791² = 55485660442255362, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (166561793) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 19990 + ... + 27068.

It is an arithmetic number, because the mean of its divisors is an integer number (8156160).

Almost surely, 2^166561791 is an apocalyptic number.

166561791 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

166561791 is a deficient number, since it is larger than the sum of its proper divisors (94435329).

166561791 is a wasteful number, since it uses less digits than its factorization.

166561791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7147.

The product of its digits is 68040, while the sum is 42.

The square root of 166561791 is about 12905.8820310740. The cubic root of 166561791 is about 550.2057533217.

The spelling of 166561791 in words is "one hundred sixty-six million, five hundred sixty-one thousand, seven hundred ninety-one".