81539979 has 4 divisors (see below), whose sum is σ = 108719976. Its totient is φ = 54359984.

The previous prime is 81539977. The next prime is 81539987. The reversal of 81539979 is 97993518.

It is a happy number.

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 81539979 - 2¹ = 81539977 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81539977) 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, 13589994 + ... + 13589999.

It is an arithmetic number, because the mean of its divisors is an integer number (27179994).

Almost surely, 2^81539979 is an apocalyptic number.

81539979 is a deficient number, since it is larger than the sum of its proper divisors (27179997).

81539979 is a wasteful number, since it uses less digits than its factorization.

81539979 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27179996.

The product of its digits is 612360, while the sum is 51.

The square root of 81539979 is about 9029.9490031783. The cubic root of 81539979 is about 433.6342047919.

The spelling of 81539979 in words is "eighty-one million, five hundred thirty-nine thousand, nine hundred seventy-nine".