81818309521 has 9 divisors (see below), whose sum is σ = 88600184379. Its totient is φ = 75521160936.

The previous prime is 81818309513. The next prime is 81818309569. The reversal of 81818309521 is 12590381818.

The square root of 81818309521 is 286039.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 12103300225 + 69715009296 = 110015^2 + 264036^2 .

It is not a de Polignac number, because 81818309521 - 2³ = 81818309513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81818309501) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 3707506 + ... + 3729508.

It is an arithmetic number, because the mean of its divisors is an integer number (9844464931).

Almost surely, 2^81818309521 is an apocalyptic number.

81818309521 is the 286039-th square number.

81818309521 is the 143020-th centered octagonal number.

It is an amenable number.

81818309521 is a deficient number, since it is larger than the sum of its proper divisors (6781874858).

81818309521 is an frugal number, since it uses more digits than its factorization.

81818309521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44032 (or 22016 counting only the distinct ones).

The product of its (nonzero) digits is 138240, while the sum is 46.

The spelling of 81818309521 in words is "eighty-one billion, eight hundred eighteen million, three hundred nine thousand, five hundred twenty-one".