16721257517 has 4 divisors (see below), whose sum is σ = 16721594556. Its totient is φ = 16720920480.

The previous prime is 16721257513. The next prime is 16721257519. The reversal of 16721257517 is 71575212761.

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 10498256521 + 6223000996 = 102461^2 + 78886^2 .

It is a cyclic number.

It is not a de Polignac number, because 16721257517 - 2² = 16721257513 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16721257513) 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, 77834 + ... + 198747.

It is an arithmetic number, because the mean of its divisors is an integer number (4180398639).

Almost surely, 2^16721257517 is an apocalyptic number.

It is an amenable number.

16721257517 is a deficient number, since it is larger than the sum of its proper divisors (337039).

16721257517 is an equidigital number, since it uses as much as digits as its factorization.

16721257517 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 337038.

The product of its digits is 205800, while the sum is 44.

The spelling of 16721257517 in words is "sixteen billion, seven hundred twenty-one million, two hundred fifty-seven thousand, five hundred seventeen".