81521773 has 2 divisors, whose sum is σ = 81521774. Its totient is φ = 81521772.

The previous prime is 81521771. The next prime is 81521827. The reversal of 81521773 is 37712518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 53611684 + 27910089 = 7322^2 + 5283^2 .

It is a cyclic number.

It is not a de Polignac number, because 81521773 - 2¹ = 81521771 is a prime.

Together with 81521771, 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 (81521771) 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, 40760886 + 40760887.

It is an arithmetic number, because the mean of its divisors is an integer number (40760887).

Almost surely, 2^81521773 is an apocalyptic number.

It is an amenable number.

81521773 is a deficient number, since it is larger than the sum of its proper divisors (1).

81521773 is an equidigital number, since it uses as much as digits as its factorization.

81521773 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11760, while the sum is 34.

The square root of 81521773 is about 9028.9408570441. The cubic root of 81521773 is about 433.6019288782.

The spelling of 81521773 in words is "eighty-one million, five hundred twenty-one thousand, seven hundred seventy-three".