81810520 has 48 divisors (see below), whose sum is σ = 202340880. Its totient is φ = 29747520.

The previous prime is 81810499. The next prime is 81810529. The reversal of 81810520 is 2501818.

It is a super-2 number, since 2×81810520² = 13385922365340800, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81810529) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3612 + ... + 13291.

It is an arithmetic number, because the mean of its divisors is an integer number (4215435).

Almost surely, 2^81810520 is an apocalyptic number.

It is an amenable number.

81810520 is an abundant number, since it is smaller than the sum of its proper divisors (120530360).

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

81810520 is a wasteful number, since it uses less digits than its factorization.

81810520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16936 (or 16921 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 25.

The square root of 81810520 is about 9044.9168044820. The cubic root of 81810520 is about 434.1132594606.

The spelling of 81810520 in words is "eighty-one million, eight hundred ten thousand, five hundred twenty".