81642791 has 4 divisors (see below), whose sum is σ = 85939800. Its totient is φ = 77345784.

The previous prime is 81642773. The next prime is 81642797. The reversal of 81642791 is 19724618.

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 81642791 - 2⁶ = 81642727 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81642797) 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, 2148476 + ... + 2148513.

It is an arithmetic number, because the mean of its divisors is an integer number (21484950).

Almost surely, 2^81642791 is an apocalyptic number.

81642791 is a deficient number, since it is larger than the sum of its proper divisors (4297009).

81642791 is a wasteful number, since it uses less digits than its factorization.

81642791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4297008.

The product of its digits is 24192, while the sum is 38.

The square root of 81642791 is about 9035.6400437379. The cubic root of 81642791 is about 433.8163815830.

The spelling of 81642791 in words is "eighty-one million, six hundred forty-two thousand, seven hundred ninety-one".