81997664 has 96 divisors (see below), whose sum is σ = 199112256. Its totient is φ = 32440320.

The previous prime is 81997633. The next prime is 81997667. The reversal of 81997664 is 46679918.

Its product of digits (653184) is a multiple of the sum of its prime factors (448).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81997667) 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 15 ways as a sum of consecutive naturals, for example, 232112 + ... + 232464.

It is an arithmetic number, because the mean of its divisors is an integer number (2074086).

Almost surely, 2^81997664 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81997664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (99556128).

81997664 is an abundant number, since it is smaller than the sum of its proper divisors (117114592).

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

81997664 is a wasteful number, since it uses less digits than its factorization.

81997664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 448 (or 440 counting only the distinct ones).

The product of its digits is 653184, while the sum is 50.

The square root of 81997664 is about 9055.2561531963. The cubic root of 81997664 is about 434.4440230463. Note that the first 3 decimals are identical.

The spelling of 81997664 in words is "eighty-one million, nine hundred ninety-seven thousand, six hundred sixty-four".