81909161 has 4 divisors (see below), whose sum is σ = 84551424. Its totient is φ = 79266900.

The previous prime is 81909151. The next prime is 81909173. The reversal of 81909161 is 16190918.

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, and also an emirpimes, since its reverse is a distinct semiprime: 16190918 = 2 ⋅8095459.

It is a cyclic number.

It is not a de Polignac number, because 81909161 - 2¹⁰ = 81908137 is a prime.

It is a super-2 number, since 2×81909161² = 13418221311447842, which contains 22 as substring.

It is a Duffinian 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, 1321085 + ... + 1321146.

It is an arithmetic number, because the mean of its divisors is an integer number (21137856).

Almost surely, 2^81909161 is an apocalyptic number.

It is an amenable number.

81909161 is a deficient number, since it is larger than the sum of its proper divisors (2642263).

81909161 is a wasteful number, since it uses less digits than its factorization.

81909161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2642262.

The product of its (nonzero) digits is 3888, while the sum is 35.

The square root of 81909161 is about 9050.3680035676. The cubic root of 81909161 is about 434.2876631407.

The spelling of 81909161 in words is "eighty-one million, nine hundred nine thousand, one hundred sixty-one".