21720355038517 has 4 divisors (see below), whose sum is σ = 22250119795596. Its totient is φ = 21190590281440.

The previous prime is 21720355038509. The next prime is 21720355038523. The reversal of 21720355038517 is 71583055302712.

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 1354909968036 + 20365445070481 = 1164006^2 + 4512809^2 .

It is a cyclic number.

It is not a de Polignac number, because 21720355038517 - 2³ = 21720355038509 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 (21720355038527) 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, 264882378478 + ... + 264882378559.

It is an arithmetic number, because the mean of its divisors is an integer number (5562529948899).

Almost surely, 2^{21720355038517} is an apocalyptic number.

It is an amenable number.

21720355038517 is a deficient number, since it is larger than the sum of its proper divisors (529764757079).

21720355038517 is an equidigital number, since it uses as much as digits as its factorization.

21720355038517 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 529764757078.

The product of its (nonzero) digits is 1764000, while the sum is 49.

The spelling of 21720355038517 in words is "twenty-one trillion, seven hundred twenty billion, three hundred fifty-five million, thirty-eight thousand, five hundred seventeen".