81359521 has 2 divisors, whose sum is σ = 81359522. Its totient is φ = 81359520.

The previous prime is 81359519. The next prime is 81359527. The reversal of 81359521 is 12595318.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 44890000 + 36469521 = 6700^2 + 6039^2 .

It is a cyclic number.

It is not a de Polignac number, because 81359521 - 2¹ = 81359519 is a prime.

Together with 81359519, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81359527) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40679760 + 40679761.

It is an arithmetic number, because the mean of its divisors is an integer number (40679761).

Almost surely, 2^81359521 is an apocalyptic number.

It is an amenable number.

81359521 is a deficient number, since it is larger than the sum of its proper divisors (1).

81359521 is an equidigital number, since it uses as much as digits as its factorization.

81359521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10800, while the sum is 34.

The square root of 81359521 is about 9019.9512748130. The cubic root of 81359521 is about 433.3140732400.

The spelling of 81359521 in words is "eighty-one million, three hundred fifty-nine thousand, five hundred twenty-one".