6516721 has 4 divisors (see below), whose sum is σ = 6639732. Its totient is φ = 6393712.

The previous prime is 6516703. The next prime is 6516739. The reversal of 6516721 is 1276156.

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

It is an interprime number because it is at equal distance from previous prime (6516703) and next prime (6516739).

It can be written as a sum of positive squares in 2 ways, for example, as 5640625 + 876096 = 2375^2 + 936^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6516721 is a prime.

It is a Duffinian number.

6516721 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 6516721.

It is not an unprimeable number, because it can be changed into a prime (6516701) 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, 61426 + ... + 61531.

It is an arithmetic number, because the mean of its divisors is an integer number (1659933).

Almost surely, 2^6516721 is an apocalyptic number.

It is an amenable number.

6516721 is a deficient number, since it is larger than the sum of its proper divisors (123011).

6516721 is a wasteful number, since it uses less digits than its factorization.

6516721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 123010.

The product of its digits is 2520, while the sum is 28.

The square root of 6516721 is about 2552.7869084591. The cubic root of 6516721 is about 186.7854498370.

The spelling of 6516721 in words is "six million, five hundred sixteen thousand, seven hundred twenty-one".