81810720 has 72 divisors (see below), whose sum is σ = 279183996. Its totient is φ = 21815808.

The previous prime is 81810719. The next prime is 81810731. The reversal of 81810720 is 2701818.

It can be written as a sum of positive squares in 2 ways, for example, as 76108176 + 5702544 = 8724^2 + 2388^2 .

It is a tau number, because it is divible by the number of its divisors (72).

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 26967 + ... + 29846.

Almost surely, 2^81810720 is an apocalyptic number.

81810720 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81810720 is an abundant number, since it is smaller than the sum of its proper divisors (197373276).

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

81810720 is a wasteful number, since it uses less digits than its factorization.

81810720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56834 (or 56823 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 27.

The square root of 81810720 is about 9044.9278604088. The cubic root of 81810720 is about 434.1136132153.

The spelling of 81810720 in words is "eighty-one million, eight hundred ten thousand, seven hundred twenty".