81815550 has 24 divisors (see below), whose sum is σ = 202902936. Its totient is φ = 21817440.

The previous prime is 81815537. The next prime is 81815557. The reversal of 81815550 is 5551818.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81815557) 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, 272569 + ... + 272868.

It is an arithmetic number, because the mean of its divisors is an integer number (8454289).

Almost surely, 2^81815550 is an apocalyptic number.

81815550 is an abundant number, since it is smaller than the sum of its proper divisors (121087386).

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

81815550 is a wasteful number, since it uses less digits than its factorization.

81815550 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 545452 (or 545447 counting only the distinct ones).

The product of its (nonzero) digits is 8000, while the sum is 33.

The square root of 81815550 is about 9045.1948569392. The cubic root of 81815550 is about 434.1221562176.

It can be divided in two parts, 8181 and 5550, that added together give a palindrome (13731).

The spelling of 81815550 in words is "eighty-one million, eight hundred fifteen thousand, five hundred fifty".