816985721 has 4 divisors (see below), whose sum is σ = 836912244. Its totient is φ = 797059200.

The previous prime is 816985717. The next prime is 816985723. The reversal of 816985721 is 127589618.

816985721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 25351225 + 791634496 = 5035^2 + 28136^2 .

It is a cyclic number.

It is not a de Polignac number, because 816985721 - 2² = 816985717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (816985723) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9963200 + ... + 9963281.

It is an arithmetic number, because the mean of its divisors is an integer number (209228061).

Almost surely, 2^816985721 is an apocalyptic number.

It is an amenable number.

816985721 is a deficient number, since it is larger than the sum of its proper divisors (19926523).

816985721 is a wasteful number, since it uses less digits than its factorization.

816985721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19926522.

The product of its digits is 241920, while the sum is 47.

The square root of 816985721 is about 28582.9620753343. The cubic root of 816985721 is about 934.8418697950.

The spelling of 816985721 in words is "eight hundred sixteen million, nine hundred eighty-five thousand, seven hundred twenty-one".