81665851 has 2 divisors, whose sum is σ = 81665852. Its totient is φ = 81665850.

The previous prime is 81665797. The next prime is 81665869. The reversal of 81665851 is 15856618.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81665851 - 2⁷ = 81665723 is a prime.

It is a super-2 number, since 2×81665851² = 13338622439108402, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81665251) 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, 40832925 + 40832926.

It is an arithmetic number, because the mean of its divisors is an integer number (40832926).

Almost surely, 2^81665851 is an apocalyptic number.

81665851 is a deficient number, since it is larger than the sum of its proper divisors (1).

81665851 is an equidigital number, since it uses as much as digits as its factorization.

81665851 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 57600, while the sum is 40.

The square root of 81665851 is about 9036.9160115606. The cubic root of 81665851 is about 433.8572215393.

The spelling of 81665851 in words is "eighty-one million, six hundred sixty-five thousand, eight hundred fifty-one".