81999216 has 200 divisors, whose sum is σ = 265510784. Its totient is φ = 24261120.

The previous prime is 81999199. The next prime is 81999217. The reversal of 81999216 is 61299918.

It is a super-2 number, since 2×81999216² = 13447742849229312, which contains 22 as substring.

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81999217) 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 39 ways as a sum of consecutive naturals, for example, 522210 + ... + 522366.

Almost surely, 2^81999216 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 81999216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (132755392).

81999216 is an abundant number, since it is smaller than the sum of its proper divisors (183511568).

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

81999216 is a wasteful number, since it uses less digits than its factorization.

81999216 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 221 (or 206 counting only the distinct ones).

The product of its digits is 69984, while the sum is 45.

The square root of 81999216 is about 9055.3418488757. The cubic root of 81999216 is about 434.4467639897.

It can be divided in two parts, 81999 and 216, that added together give a triangular number (82215 = T₄₀₅).

The spelling of 81999216 in words is "eighty-one million, nine hundred ninety-nine thousand, two hundred sixteen".