81997440 has 128 divisors (see below), whose sum is σ = 298753920. Its totient is φ = 18739200.

The previous prime is 81997429. The next prime is 81997441. The reversal of 81997440 is 4479918.

It is a tau number, because it is divible by the number of its divisors (128).

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a junction number, because it is equal to n+sod(n) for n = 81997392 and 81997401.

It is not an unprimeable number, because it can be changed into a prime (81997441) 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 15 ways as a sum of consecutive naturals, for example, 10390 + ... + 16490.

It is an arithmetic number, because the mean of its divisors is an integer number (2334015).

Almost surely, 2^81997440 is an apocalyptic number.

81997440 is a gapful number since it is divisible by the number (80) 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 81997440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (149376960).

81997440 is an abundant number, since it is smaller than the sum of its proper divisors (216756480).

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

81997440 is a wasteful number, since it uses less digits than its factorization.

81997440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6130 (or 6118 counting only the distinct ones).

The product of its (nonzero) digits is 72576, while the sum is 42.

The square root of 81997440 is about 9055.2437846808. The cubic root of 81997440 is about 434.4436274434.

The spelling of 81997440 in words is "eighty-one million, nine hundred ninety-seven thousand, four hundred forty".