81811236 has 48 divisors (see below), whose sum is σ = 210607488. Its totient is φ = 24556800.

The previous prime is 81811231. The next prime is 81811267. The reversal of 81811236 is 63211818.

81811236 is a nontrivial binomial coefficient, being equal to C(12792, 2).

It is not an unprimeable number, because it can be changed into a prime (81811231) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1 + ... + 12791.

It is an arithmetic number, because the mean of its divisors is an integer number (4387656).

Almost surely, 2^81811236 is an apocalyptic number.

81811236 is the 12791-st triangular number and also the 6396-th hexagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81811236, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (105303744).

81811236 is an abundant number, since it is smaller than the sum of its proper divisors (128796252).

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

81811236 is a wasteful number, since it uses less digits than its factorization.

81811236 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12852 (or 12850 counting only the distinct ones).

The product of its digits is 2304, while the sum is 30.

The square root of 81811236 is about 9044.9563846378. The cubic root of 81811236 is about 434.1145258999.

The spelling of 81811236 in words is "eighty-one million, eight hundred eleven thousand, two hundred thirty-six".