15511642721 has 4 divisors (see below), whose sum is σ = 15665223444. Its totient is φ = 15358062000.

The previous prime is 15511642717. The next prime is 15511642733. The reversal of 15511642721 is 12724611551.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12724611551 = 71 ⋅179219881.

It can be written as a sum of positive squares in 2 ways, for example, as 14821845025 + 689797696 = 121745^2 + 26264^2 .

It is a cyclic number.

It is not a de Polignac number, because 15511642721 - 2² = 15511642717 is a prime.

It is a super-2 number, since 2×15511642721² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (15511642621) 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, 76790210 + ... + 76790411.

It is an arithmetic number, because the mean of its divisors is an integer number (3916305861).

Almost surely, 2^15511642721 is an apocalyptic number.

It is an amenable number.

15511642721 is a deficient number, since it is larger than the sum of its proper divisors (153580723).

15511642721 is a wasteful number, since it uses less digits than its factorization.

15511642721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 153580722.

The product of its digits is 16800, while the sum is 35.

The spelling of 15511642721 in words is "fifteen billion, five hundred eleven million, six hundred forty-two thousand, seven hundred twenty-one".