15555550721 has 4 divisors (see below), whose sum is σ = 15849051732. Its totient is φ = 15262049712.

The previous prime is 15555550711. The next prime is 15555550789. The reversal of 15555550721 is 12705555551.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12705555551 = 13 ⋅977350427.

It can be written as a sum of positive squares in 2 ways, for example, as 4950670321 + 10604880400 = 70361^2 + 102980^2 .

It is a cyclic number.

It is not a de Polignac number, because 15555550721 - 2⁶ = 15555550657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (15555550711) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 146750426 + ... + 146750531.

It is an arithmetic number, because the mean of its divisors is an integer number (3962262933).

Almost surely, 2^15555550721 is an apocalyptic number.

It is an amenable number.

15555550721 is a deficient number, since it is larger than the sum of its proper divisors (293501011).

15555550721 is an equidigital number, since it uses as much as digits as its factorization.

15555550721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 293501010.

The product of its (nonzero) digits is 218750, while the sum is 41.

The spelling of 15555550721 in words is "fifteen billion, five hundred fifty-five million, five hundred fifty thousand, seven hundred twenty-one".