81780091 has 4 divisors (see below), whose sum is σ = 81817992. Its totient is φ = 81742192.

The previous prime is 81780071. The next prime is 81780103. The reversal of 81780091 is 19008718.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81780091 - 2⁵ = 81780059 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81780011) 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, 15505 + ... + 20098.

It is an arithmetic number, because the mean of its divisors is an integer number (20454498).

Almost surely, 2^81780091 is an apocalyptic number.

81780091 is a deficient number, since it is larger than the sum of its proper divisors (37901).

81780091 is a wasteful number, since it uses less digits than its factorization.

81780091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37900.

The product of its (nonzero) digits is 4032, while the sum is 34.

The square root of 81780091 is about 9043.2345430161. The cubic root of 81780091 is about 434.0594307253.

It can be divided in two parts, 817 and 80091, that added together give a palindrome (80908).

The spelling of 81780091 in words is "eighty-one million, seven hundred eighty thousand, ninety-one".