81131851609 has 16 divisors (see below), whose sum is σ = 84706779024. Its totient is φ = 77633920000.

The previous prime is 81131851601. The next prime is 81131851613. The reversal of 81131851609 is 90615813118.

It can be written as a sum of positive squares in 8 ways, for example, as 2028601600 + 79103250009 = 45040^2 + 281253^2 .

It is a cyclic number.

It is not a de Polignac number, because 81131851609 - 2³ = 81131851601 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81131851601) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11585109 + ... + 11592109.

It is an arithmetic number, because the mean of its divisors is an integer number (5294173689).

Almost surely, 2^81131851609 is an apocalyptic number.

It is an amenable number.

81131851609 is a deficient number, since it is larger than the sum of its proper divisors (3574927415).

81131851609 is a wasteful number, since it uses less digits than its factorization.

81131851609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12428.

The product of its (nonzero) digits is 51840, while the sum is 43.

The spelling of 81131851609 in words is "eighty-one billion, one hundred thirty-one million, eight hundred fifty-one thousand, six hundred nine".