81331664 has 20 divisors (see below), whose sum is σ = 159143460. Its totient is φ = 40262400.

The previous prime is 81331651. The next prime is 81331669. The reversal of 81331664 is 46613318.

It can be written as a sum of positive squares in 2 ways, for example, as 35904064 + 45427600 = 5992^2 + 6740^2 .

It is a super-2 number, since 2×81331664² = 13229679138017792, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 81331664.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81331669) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 23549 + ... + 26780.

It is an arithmetic number, because the mean of its divisors is an integer number (7957173).

Almost surely, 2^81331664 is an apocalyptic number.

It is an amenable number.

81331664 is a deficient number, since it is larger than the sum of its proper divisors (77811796).

81331664 is a wasteful number, since it uses less digits than its factorization.

81331664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50438 (or 50432 counting only the distinct ones).

The product of its digits is 10368, while the sum is 32.

The square root of 81331664 is about 9018.4069546678. The cubic root of 81331664 is about 433.2646129026.

The spelling of 81331664 in words is "eighty-one million, three hundred thirty-one thousand, six hundred sixty-four".