81918720 has 216 divisors, whose sum is σ = 305790576. Its totient is φ = 20127744.

The previous prime is 81918713. The next prime is 81918737. The reversal of 81918720 is 2781918.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 149487 + ... + 150033.

Almost surely, 2^81918720 is an apocalyptic number.

81918720 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 81918720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (152895288).

81918720 is an abundant number, since it is smaller than the sum of its proper divisors (223871856).

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

81918720 is a wasteful number, since it uses less digits than its factorization.

81918720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 587 (or 570 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 81918720 is about 9050.8960882335. The cubic root of 81918720 is about 434.3045566287.

The spelling of 81918720 in words is "eighty-one million, nine hundred eighteen thousand, seven hundred twenty".