81666019 has 2 divisors, whose sum is σ = 81666020. Its totient is φ = 81666018.

The previous prime is 81666017. The next prime is 81666023. The reversal of 81666019 is 91066618.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81666019 - 2¹ = 81666017 is a prime.

It is a super-2 number, since 2×81666019² = 13338677318616722, which contains 22 as substring.

Together with 81666017, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81666017) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40833009 + 40833010.

It is an arithmetic number, because the mean of its divisors is an integer number (40833010).

Almost surely, 2^81666019 is an apocalyptic number.

81666019 is a deficient number, since it is larger than the sum of its proper divisors (1).

81666019 is an equidigital number, since it uses as much as digits as its factorization.

81666019 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 15552, while the sum is 37.

The square root of 81666019 is about 9036.9253067623. The cubic root of 81666019 is about 433.8575190441.

The spelling of 81666019 in words is "eighty-one million, six hundred sixty-six thousand, nineteen".