81689664 has 168 divisors, whose sum is σ = 265236960. Its totient is φ = 22063104.

The previous prime is 81689653. The next prime is 81689669. The reversal of 81689664 is 46698618.

It is a tau number, because it is divible by the number of its divisors (168).

It is a Harshad number since it is a multiple of its sum of digits (48).

It is not an unprimeable number, because it can be changed into a prime (81689669) 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 in 23 ways as a sum of consecutive naturals, for example, 178524 + ... + 178980.

Almost surely, 2^81689664 is an apocalyptic number.

81689664 is a gapful number since it is divisible by the number (84) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81689664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (132618480).

81689664 is an abundant number, since it is smaller than the sum of its proper divisors (183547296).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81689664 is a wasteful number, since it uses less digits than its factorization.

81689664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 505 (or 488 counting only the distinct ones).

The product of its digits is 497664, while the sum is 48.

The square root of 81689664 is about 9038.2334557147. The cubic root of 81689664 is about 433.8993870134.

The spelling of 81689664 in words is "eighty-one million, six hundred eighty-nine thousand, six hundred sixty-four".