81979009 has 12 divisors (see below), whose sum is σ = 96244500. Its totient is φ = 69618528.

The previous prime is 81978997. The next prime is 81979043. The reversal of 81979009 is 90097918.

It can be written as a sum of positive squares in 2 ways, for example, as 42289009 + 39690000 = 6503^2 + 6300^2 .

It is not a de Polignac number, because 81979009 - 2⁹ = 81978497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81979099) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2334 + ... + 13015.

It is an arithmetic number, because the mean of its divisors is an integer number (8020375).

Almost surely, 2^81979009 is an apocalyptic number.

It is an amenable number.

81979009 is a deficient number, since it is larger than the sum of its proper divisors (14265491).

81979009 is a wasteful number, since it uses less digits than its factorization.

81979009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15472 (or 15465 counting only the distinct ones).

The product of its (nonzero) digits is 40824, while the sum is 43.

The square root of 81979009 is about 9054.2260298714. The cubic root of 81979009 is about 434.4110742705.

The spelling of 81979009 in words is "eighty-one million, nine hundred seventy-nine thousand, nine".