81172091 has 32 divisors (see below), whose sum is σ = 110412288. Its totient is φ = 57623040.

The previous prime is 81172079. The next prime is 81172103. The reversal of 81172091 is 19027118.

It is an interprime number because it is at equal distance from previous prime (81172079) and next prime (81172103).

It is a cyclic number.

It is not a de Polignac number, because 81172091 - 2²⁶ = 14063227 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81172001) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 82595 + ... + 83571.

It is an arithmetic number, because the mean of its divisors is an integer number (3450384).

Almost surely, 2^81172091 is an apocalyptic number.

81172091 is a deficient number, since it is larger than the sum of its proper divisors (29240197).

81172091 is a wasteful number, since it uses less digits than its factorization.

81172091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1091.

The product of its (nonzero) digits is 1008, while the sum is 29.

The square root of 81172091 is about 9009.5555384270. Note that the first 4 decimals coincide. The cubic root of 81172091 is about 432.9810718400.

The spelling of 81172091 in words is "eighty-one million, one hundred seventy-two thousand, ninety-one".