81211816 has 96 divisors (see below), whose sum is σ = 188455680. Its totient is φ = 32659200.

The previous prime is 81211813. The next prime is 81211829. The reversal of 81211816 is 61811218.

It is a hoax number, since the sum of its digits (28) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81211811) 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 23 ways as a sum of consecutive naturals, for example, 498151 + ... + 498313.

It is an arithmetic number, because the mean of its divisors is an integer number (1963080).

Almost surely, 2^81211816 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 81211816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (94227840).

81211816 is an abundant number, since it is smaller than the sum of its proper divisors (107243864).

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

81211816 is a wasteful number, since it uses less digits than its factorization.

81211816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 255 (or 244 counting only the distinct ones).

The product of its digits is 768, while the sum is 28.

The square root of 81211816 is about 9011.7598725221. The cubic root of 81211816 is about 433.0516928615.

The spelling of 81211816 in words is "eighty-one million, two hundred eleven thousand, eight hundred sixteen".