81686993 has 2 divisors, whose sum is σ = 81686994. Its totient is φ = 81686992.

The previous prime is 81686977. The next prime is 81687017. The reversal of 81686993 is 39968618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 47018449 + 34668544 = 6857^2 + 5888^2 .

It is a cyclic number.

It is not a de Polignac number, because 81686993 - 2⁴ = 81686977 is a prime.

It is not a weakly prime, because it can be changed into another prime (81686933) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40843496 + 40843497.

It is an arithmetic number, because the mean of its divisors is an integer number (40843497).

Almost surely, 2^81686993 is an apocalyptic number.

It is an amenable number.

81686993 is a deficient number, since it is larger than the sum of its proper divisors (1).

81686993 is an equidigital number, since it uses as much as digits as its factorization.

81686993 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 559872, while the sum is 50.

The square root of 81686993 is about 9038.0856933313. The cubic root of 81686993 is about 433.8946579048.

The spelling of 81686993 in words is "eighty-one million, six hundred eighty-six thousand, nine hundred ninety-three".