81009989 has 4 divisors (see below), whose sum is σ = 81457740. Its totient is φ = 80562240.

The previous prime is 81009961. The next prime is 81010001. The reversal of 81009989 is 98990018.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3833764 + 77176225 = 1958^2 + 8785^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81009989 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 (81009389) 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, 223604 + ... + 223965.

It is an arithmetic number, because the mean of its divisors is an integer number (20364435).

Almost surely, 2^81009989 is an apocalyptic number.

It is an amenable number.

81009989 is a deficient number, since it is larger than the sum of its proper divisors (447751).

81009989 is a wasteful number, since it uses less digits than its factorization.

81009989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 447750.

The product of its (nonzero) digits is 46656, while the sum is 44.

The square root of 81009989 is about 9000.5549273364. The cubic root of 81009989 is about 432.6926563253.

The spelling of 81009989 in words is "eighty-one million, nine thousand, nine hundred eighty-nine".