81015891 has 16 divisors (see below), whose sum is σ = 118213248. Its totient is φ = 48945600.

The previous prime is 81015887. The next prime is 81015901. The reversal of 81015891 is 19851018.

It is not a de Polignac number, because 81015891 - 2² = 81015887 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is not an unprimeable number, because it can be changed into a prime (81015841) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7215 + ... + 14631.

It is an arithmetic number, because the mean of its divisors is an integer number (7388328).

Almost surely, 2^81015891 is an apocalyptic number.

81015891 is a deficient number, since it is larger than the sum of its proper divisors (37197357).

81015891 is a wasteful number, since it uses less digits than its factorization.

81015891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7762.

The product of its (nonzero) digits is 2880, while the sum is 33.

The square root of 81015891 is about 9000.8827900379. The cubic root of 81015891 is about 432.7031640420.

The spelling of 81015891 in words is "eighty-one million, fifteen thousand, eight hundred ninety-one".