216839721 has 16 divisors (see below), whose sum is σ = 339353984. Its totient is φ = 120559104.

The previous prime is 216839713. The next prime is 216839731. The reversal of 216839721 is 127938612.

It is not a de Polignac number, because 216839721 - 2³ = 216839713 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 216839721.

It is not an unprimeable number, because it can be changed into a prime (216839731) 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, 138760 + ... + 140313.

It is an arithmetic number, because the mean of its divisors is an integer number (21209624).

Almost surely, 2^216839721 is an apocalyptic number.

216839721 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

216839721 is a deficient number, since it is larger than the sum of its proper divisors (122514263).

216839721 is a wasteful number, since it uses less digits than its factorization.

216839721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 279120.

The product of its digits is 36288, while the sum is 39.

The square root of 216839721 is about 14725.4786339867. The cubic root of 216839721 is about 600.7765140541.

The spelling of 216839721 in words is "two hundred sixteen million, eight hundred thirty-nine thousand, seven hundred twenty-one".