81809999 has 2 divisors, whose sum is σ = 81810000. Its totient is φ = 81809998.

The previous prime is 81809993. The next prime is 81810007. The reversal of 81809999 is 99990818.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81809999 - 2⁸ = 81809743 is a prime.

81809999 is a modest number, since divided by 9999 gives 8180 as remainder.

It is a self number, because there is not a number n which added to its sum of digits gives 81809999.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81809993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40904999 + 40905000.

It is an arithmetic number, because the mean of its divisors is an integer number (40905000).

Almost surely, 2^81809999 is an apocalyptic number.

81809999 is a deficient number, since it is larger than the sum of its proper divisors (1).

81809999 is an equidigital number, since it uses as much as digits as its factorization.

81809999 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 419904, while the sum is 53.

The square root of 81809999 is about 9044.8880037290. Note that the first 3 decimals coincide. The cubic root of 81809999 is about 434.1123379267.

The spelling of 81809999 in words is "eighty-one million, eight hundred nine thousand, nine hundred ninety-nine".