81581709 has 12 divisors (see below), whose sum is σ = 119563808. Its totient is φ = 49443240.

The previous prime is 81581693. The next prime is 81581711. The reversal of 81581709 is 90718518.

It is not a de Polignac number, because 81581709 - 2⁴ = 81581693 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81581749) 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, 112009 + ... + 112734.

Almost surely, 2^81581709 is an apocalyptic number.

It is an amenable number.

81581709 is a deficient number, since it is larger than the sum of its proper divisors (37982099).

81581709 is a wasteful number, since it uses less digits than its factorization.

81581709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 224768 (or 224757 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 39.

The square root of 81581709 is about 9032.2593519008. The cubic root of 81581709 is about 433.7081663403.

The spelling of 81581709 in words is "eighty-one million, five hundred eighty-one thousand, seven hundred nine".