81850991 has 2 divisors, whose sum is σ = 81850992. Its totient is φ = 81850990.

The previous prime is 81850987. The next prime is 81850999. The reversal of 81850991 is 19905818.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81850991 - 2² = 81850987 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81850999) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40925495 + 40925496.

It is an arithmetic number, because the mean of its divisors is an integer number (40925496).

Almost surely, 2^81850991 is an apocalyptic number.

81850991 is a deficient number, since it is larger than the sum of its proper divisors (1).

81850991 is an equidigital number, since it uses as much as digits as its factorization.

81850991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 25920, while the sum is 41.

The square root of 81850991 is about 9047.1537513187. The cubic root of 81850991 is about 434.1848317614.

The spelling of 81850991 in words is "eighty-one million, eight hundred fifty thousand, nine hundred ninety-one".