81440720 has 40 divisors (see below), whose sum is σ = 195463680. Its totient is φ = 31524480.

The previous prime is 81440717. The next prime is 81440759. The reversal of 81440720 is 2704418.

It is a tau number, because it is divible by the number of its divisors (40).

It is a self number, because there is not a number n which added to its sum of digits gives 81440720.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13940 + ... + 18899.

It is an arithmetic number, because the mean of its divisors is an integer number (4886592).

Almost surely, 2^81440720 is an apocalyptic number.

81440720 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81440720 is an abundant number, since it is smaller than the sum of its proper divisors (114022960).

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

81440720 is a wasteful number, since it uses less digits than its factorization.

81440720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32883 (or 32877 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 26.

The square root of 81440720 is about 9024.4512298533. The cubic root of 81440720 is about 433.4581783609.

The spelling of 81440720 in words is "eighty-one million, four hundred forty thousand, seven hundred twenty".