81191909 has 8 divisors (see below), whose sum is σ = 87644160. Its totient is φ = 74983216.

The previous prime is 81191897. The next prime is 81191911. The reversal of 81191909 is 90919118.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81191909 - 2²⁰ = 80143333 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 (81191939) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 60197 + ... + 61530.

It is an arithmetic number, because the mean of its divisors is an integer number (10955520).

Almost surely, 2^81191909 is an apocalyptic number.

It is an amenable number.

81191909 is a deficient number, since it is larger than the sum of its proper divisors (6452251).

81191909 is a wasteful number, since it uses less digits than its factorization.

81191909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 121779.

The product of its (nonzero) digits is 5832, while the sum is 38.

The square root of 81191909 is about 9010.6553035836. The cubic root of 81191909 is about 433.0163061204.

The spelling of 81191909 in words is "eighty-one million, one hundred ninety-one thousand, nine hundred nine".