163865581 has 18 divisors (see below), whose sum is σ = 184306346. Its totient is φ = 145543200.

The previous prime is 163865579. The next prime is 163865587. The reversal of 163865581 is 185568361.

It can be written as a sum of positive squares in 3 ways, for example, as 18783556 + 145082025 = 4334^2 + 12045^2 .

It is not a de Polignac number, because 163865581 - 2¹ = 163865579 is a prime.

It is a super-2 number, since 2×163865581² = 53703857272935122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (163865587) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 1099695 + ... + 1099843.

Almost surely, 2^163865581 is an apocalyptic number.

163865581 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

163865581 is a deficient number, since it is larger than the sum of its proper divisors (20440765).

163865581 is an equidigital number, since it uses as much as digits as its factorization.

163865581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 381 (or 221 counting only the distinct ones).

The product of its digits is 172800, while the sum is 43.

The square root of 163865581 is about 12800.9992188110. Note that the first 3 decimals coincide. The cubic root of 163865581 is about 547.2207799016.

The spelling of 163865581 in words is "one hundred sixty-three million, eight hundred sixty-five thousand, five hundred eighty-one".