81249691 has 4 divisors (see below), whose sum is σ = 81330912. Its totient is φ = 81168472.

The previous prime is 81249671. The next prime is 81249713. The reversal of 81249691 is 19694218.

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 81249691 - 2⁷ = 81249563 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81249611) 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, 39091 + ... + 41116.

It is an arithmetic number, because the mean of its divisors is an integer number (20332728).

Almost surely, 2^81249691 is an apocalyptic number.

81249691 is a deficient number, since it is larger than the sum of its proper divisors (81221).

81249691 is a wasteful number, since it uses less digits than its factorization.

81249691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 81220.

The product of its digits is 31104, while the sum is 40.

The square root of 81249691 is about 9013.8610484076. The cubic root of 81249691 is about 433.1190036074.

The spelling of 81249691 in words is "eighty-one million, two hundred forty-nine thousand, six hundred ninety-one".