81640189 has 4 divisors (see below), whose sum is σ = 81658300. Its totient is φ = 81622080.

The previous prime is 81640183. The next prime is 81640201. The reversal of 81640189 is 98104618.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 98104618 = 2 ⋅49052309.

It can be written as a sum of positive squares in 2 ways, for example, as 37417689 + 44222500 = 6117^2 + 6650^2 .

It is a cyclic number.

It is not a de Polignac number, because 81640189 - 2¹⁹ = 81115901 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81640183) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3637 + ... + 13285.

It is an arithmetic number, because the mean of its divisors is an integer number (20414575).

Almost surely, 2^81640189 is an apocalyptic number.

It is an amenable number.

81640189 is a deficient number, since it is larger than the sum of its proper divisors (18111).

81640189 is an equidigital number, since it uses as much as digits as its factorization.

81640189 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18110.

The product of its (nonzero) digits is 13824, while the sum is 37.

The square root of 81640189 is about 9035.4960572179. The cubic root of 81640189 is about 433.8117728796.

The spelling of 81640189 in words is "eighty-one million, six hundred forty thousand, one hundred eighty-nine".