81791399 has 2 divisors, whose sum is σ = 81791400. Its totient is φ = 81791398.

The previous prime is 81791393. The next prime is 81791401. The reversal of 81791399 is 99319718.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81791399 - 2⁴ = 81791383 is a prime.

Together with 81791401, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81791393) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40895699 + 40895700.

It is an arithmetic number, because the mean of its divisors is an integer number (40895700).

Almost surely, 2^81791399 is an apocalyptic number.

81791399 is a deficient number, since it is larger than the sum of its proper divisors (1).

81791399 is an equidigital number, since it uses as much as digits as its factorization.

81791399 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 122472, while the sum is 47.

The square root of 81791399 is about 9043.8597401773. The cubic root of 81791399 is about 434.0794360745.

The spelling of 81791399 in words is "eighty-one million, seven hundred ninety-one thousand, three hundred ninety-nine".