21517741506721 has 4 divisors (see below), whose sum is σ = 21517751174932. Its totient is φ = 21517731838512.

The previous prime is 21517741506713. The next prime is 21517741506727. The reversal of 21517741506721 is 12760514771512.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 16222657285696 + 5295084221025 = 4027736^2 + 2301105^2 .

It is a cyclic number.

It is not a de Polignac number, because 21517741506721 - 2³ = 21517741506713 is a prime.

It is a super-3 number, since 3×21517741506721³ (a number of 41 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21517741506727) 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, 376375 + ... + 6570931.

It is an arithmetic number, because the mean of its divisors is an integer number (5379437793733).

Almost surely, 2^{21517741506721} is an apocalyptic number.

It is an amenable number.

21517741506721 is a deficient number, since it is larger than the sum of its proper divisors (9668211).

21517741506721 is an equidigital number, since it uses as much as digits as its factorization.

21517741506721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9668210.

The product of its (nonzero) digits is 823200, while the sum is 49.

The spelling of 21517741506721 in words is "twenty-one trillion, five hundred seventeen billion, seven hundred forty-one million, five hundred six thousand, seven hundred twenty-one".