3128040721 has 4 divisors (see below), whose sum is σ = 3368659252. Its totient is φ = 2887422192.

The previous prime is 3128040691. The next prime is 3128040767. The reversal of 3128040721 is 1270408213.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1270408213 = 593 ⋅2142341.

It can be written as a sum of positive squares in 2 ways, for example, as 1690114321 + 1437926400 = 41111^2 + 37920^2 .

It is a cyclic number.

It is not a de Polignac number, because 3128040721 - 2¹⁷ = 3127909649 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 3128040721.

It is not an unprimeable number, because it can be changed into a prime (3128040781) 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, 120309246 + ... + 120309271.

It is an arithmetic number, because the mean of its divisors is an integer number (842164813).

Almost surely, 2^3128040721 is an apocalyptic number.

It is an amenable number.

3128040721 is a deficient number, since it is larger than the sum of its proper divisors (240618531).

3128040721 is a wasteful number, since it uses less digits than its factorization.

3128040721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 240618530.

The product of its (nonzero) digits is 2688, while the sum is 28.

The square root of 3128040721 is about 55928.8898602502. The cubic root of 3128040721 is about 1462.4829085689.

Adding to 3128040721 its reverse (1270408213), we get a palindrome (4398448934).

The spelling of 3128040721 in words is "three billion, one hundred twenty-eight million, forty thousand, seven hundred twenty-one".