81689581 has 2 divisors, whose sum is σ = 81689582. Its totient is φ = 81689580.

The previous prime is 81689579. The next prime is 81689591. The reversal of 81689581 is 18598618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 56025225 + 25664356 = 7485^2 + 5066^2 .

It is a cyclic number.

It is not a de Polignac number, because 81689581 - 2¹ = 81689579 is a prime.

It is a super-2 number, since 2×81689581² = 13346375287911122, which contains 22 as substring.

Together with 81689579, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81689501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40844790 + 40844791.

It is an arithmetic number, because the mean of its divisors is an integer number (40844791).

Almost surely, 2^81689581 is an apocalyptic number.

It is an amenable number.

81689581 is a deficient number, since it is larger than the sum of its proper divisors (1).

81689581 is an equidigital number, since it uses as much as digits as its factorization.

81689581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 138240, while the sum is 46.

The square root of 81689581 is about 9038.2288641083. The cubic root of 81689581 is about 433.8992400603.

The spelling of 81689581 in words is "eighty-one million, six hundred eighty-nine thousand, five hundred eighty-one".