81811215 has 40 divisors (see below), whose sum is σ = 148568640. Its totient is φ = 43063488.

The previous prime is 81811211. The next prime is 81811231. The reversal of 81811215 is 51211818.

It is not a de Polignac number, because 81811215 - 2² = 81811211 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81811211) 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, 30717 + ... + 33273.

It is an arithmetic number, because the mean of its divisors is an integer number (3714216).

Almost surely, 2^81811215 is an apocalyptic number.

81811215 is a deficient number, since it is larger than the sum of its proper divisors (66757425).

81811215 is a wasteful number, since it uses less digits than its factorization.

81811215 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2653 (or 2644 counting only the distinct ones).

The product of its digits is 640, while the sum is 27.

The square root of 81811215 is about 9044.9552237698. The cubic root of 81811215 is about 434.1144887559.

The spelling of 81811215 in words is "eighty-one million, eight hundred eleven thousand, two hundred fifteen".