81531216 has 120 divisors (see below), whose sum is σ = 248812200. Its totient is φ = 24772608.

The previous prime is 81531211. The next prime is 81531227. The reversal of 81531216 is 61213518.

It can be written as a sum of positive squares in 4 ways, for example, as 4161600 + 77369616 = 2040^2 + 8796^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 81531216.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81531211) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 181360 + ... + 181808.

It is an arithmetic number, because the mean of its divisors is an integer number (2073435).

Almost surely, 2^81531216 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 81531216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (124406100).

81531216 is an abundant number, since it is smaller than the sum of its proper divisors (167280984).

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

81531216 is a wasteful number, since it uses less digits than its factorization.

81531216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 573 (or 564 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 81531216 is about 9029.4637714540. The cubic root of 81531216 is about 433.6186701927.

The spelling of 81531216 in words is "eighty-one million, five hundred thirty-one thousand, two hundred sixteen".