518321721 has 16 divisors (see below), whose sum is σ = 763565184. Its totient is φ = 311080704.

The previous prime is 518321719. The next prime is 518321743. The reversal of 518321721 is 127123815.

It is not a de Polignac number, because 518321721 - 2¹ = 518321719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (518321701) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 219766 + ... + 222111.

It is an arithmetic number, because the mean of its divisors is an integer number (47722824).

Almost surely, 2^518321721 is an apocalyptic number.

518321721 is a gapful number since it is divisible by the number (51) formed by its first and last digit.

It is an amenable number.

518321721 is a deficient number, since it is larger than the sum of its proper divisors (245243463).

518321721 is a wasteful number, since it uses less digits than its factorization.

518321721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 441920.

The product of its digits is 3360, while the sum is 30.

The square root of 518321721 is about 22766.6800610014. The cubic root of 518321721 is about 803.2791040031.

The spelling of 518321721 in words is "five hundred eighteen million, three hundred twenty-one thousand, seven hundred twenty-one".