81131899 has 2 divisors, whose sum is σ = 81131900. Its totient is φ = 81131898.

The previous prime is 81131893. The next prime is 81131933. The reversal of 81131899 is 99813118.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81131899 - 2²³ = 72743291 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81131893) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40565949 + 40565950.

It is an arithmetic number, because the mean of its divisors is an integer number (40565950).

Almost surely, 2^81131899 is an apocalyptic number.

81131899 is a deficient number, since it is larger than the sum of its proper divisors (1).

81131899 is an equidigital number, since it uses as much as digits as its factorization.

81131899 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 40.

The square root of 81131899 is about 9007.3247415645. The cubic root of 81131899 is about 432.9095971576.

The spelling of 81131899 in words is "eighty-one million, one hundred thirty-one thousand, eight hundred ninety-nine".