21520717813 has 4 divisors (see below), whose sum is σ = 24595106080. Its totient is φ = 18446329548.

The previous prime is 21520717789. The next prime is 21520717847. The reversal of 21520717813 is 31871702512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21520717813 - 2²¹ = 21518620661 is a prime.

It is a Duffinian number.

It is a zygodrome in base 4.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21220717813) 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, 1537194123 + ... + 1537194136.

It is an arithmetic number, because the mean of its divisors is an integer number (6148776520).

Almost surely, 2^21520717813 is an apocalyptic number.

It is an amenable number.

21520717813 is a deficient number, since it is larger than the sum of its proper divisors (3074388267).

21520717813 is an equidigital number, since it uses as much as digits as its factorization.

21520717813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3074388266.

The product of its (nonzero) digits is 23520, while the sum is 37.

The spelling of 21520717813 in words is "twenty-one billion, five hundred twenty million, seven hundred seventeen thousand, eight hundred thirteen".