81909181 has 4 divisors (see below), whose sum is σ = 82055232. Its totient is φ = 81763132.

The previous prime is 81909173. The next prime is 81909193. The reversal of 81909181 is 18190918.

It is a happy number.

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.

It is a cyclic number.

It is not a de Polignac number, because 81909181 - 2³ = 81909173 is a prime.

It is a super-2 number, since 2×81909181² = 13418227864181522, which contains 22 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 81909181.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81909151) 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, 72181 + ... + 73306.

It is an arithmetic number, because the mean of its divisors is an integer number (20513808).

Almost surely, 2^81909181 is an apocalyptic number.

It is an amenable number.

81909181 is a deficient number, since it is larger than the sum of its proper divisors (146051).

81909181 is a wasteful number, since it uses less digits than its factorization.

81909181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 146050.

The product of its (nonzero) digits is 5184, while the sum is 37.

The square root of 81909181 is about 9050.3691084950. The cubic root of 81909181 is about 434.2876984878.

It can be divided in two parts, 8190 and 9181, that added together give a palindrome (17371).

The spelling of 81909181 in words is "eighty-one million, nine hundred nine thousand, one hundred eighty-one".