1805500128721 has 3 divisors (see below), whose sum is σ = 1805501472411. Its totient is φ = 1805498785032.

The previous prime is 1805500128713. The next prime is 1805500128737. The reversal of 1805500128721 is 1278210055081.

The square root of 1805500128721 is 1343689.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 1021637799121 + 783862329600 = 1010761^2 + 885360^2 .

It is not a de Polignac number, because 1805500128721 - 2³ = 1805500128713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1805500128221) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 671845 + ... + 2015533.

It is an arithmetic number, because the mean of its divisors is an integer number (601833824137).

Almost surely, 2^{1805500128721} is an apocalyptic number.

1805500128721 is the 1343689-th square number.

1805500128721 is the 671845-th centered octagonal number.

It is an amenable number.

1805500128721 is a deficient number, since it is larger than the sum of its proper divisors (1343690).

1805500128721 is an frugal number, since it uses more digits than its factorization.

1805500128721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2687378 (or 1343689 counting only the distinct ones).

The product of its (nonzero) digits is 44800, while the sum is 40.

The spelling of 1805500128721 in words is "one trillion, eight hundred five billion, five hundred million, one hundred twenty-eight thousand, seven hundred twenty-one".