21172011517 has 4 divisors (see below), whose sum is σ = 21176426236. Its totient is φ = 21167596800.

The previous prime is 21172011473. The next prime is 21172011533. The reversal of 21172011517 is 71511027112.

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 17228925081 + 3943086436 = 131259^2 + 62794^2 .

It is a cyclic number.

It is not a de Polignac number, because 21172011517 - 2²⁷ = 21037793789 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 (21172011587) 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, 2200158 + ... + 2209759.

It is an arithmetic number, because the mean of its divisors is an integer number (5294106559).

Almost surely, 2^21172011517 is an apocalyptic number.

It is an amenable number.

21172011517 is a deficient number, since it is larger than the sum of its proper divisors (4414719).

21172011517 is an equidigital number, since it uses as much as digits as its factorization.

21172011517 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4414718.

The product of its (nonzero) digits is 980, while the sum is 28.

Adding to 21172011517 its reverse (71511027112), we get a palindrome (92683038629).

The spelling of 21172011517 in words is "twenty-one billion, one hundred seventy-two million, eleven thousand, five hundred seventeen".