21520523555 has 4 divisors (see below), whose sum is σ = 25824628272. Its totient is φ = 17216418840.

The previous prime is 21520523539. The next prime is 21520523573. The reversal of 21520523555 is 55532502512.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21520523555 - 2⁴ = 21520523539 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2152052351 + ... + 2152052360.

It is an arithmetic number, because the mean of its divisors is an integer number (6456157068).

Almost surely, 2^21520523555 is an apocalyptic number.

21520523555 is a deficient number, since it is larger than the sum of its proper divisors (4304104717).

21520523555 is an equidigital number, since it uses as much as digits as its factorization.

21520523555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4304104716.

The product of its (nonzero) digits is 75000, while the sum is 35.

The spelling of 21520523555 in words is "twenty-one billion, five hundred twenty million, five hundred twenty-three thousand, five hundred fifty-five".