21356465521 has 4 divisors (see below), whose sum is σ = 21368963700. Its totient is φ = 21343967344.

The previous prime is 21356465513. The next prime is 21356465549. The reversal of 21356465521 is 12556465312.

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 11148192225 + 10208273296 = 105585^2 + 101036^2 .

It is a cyclic number.

It is not a de Polignac number, because 21356465521 - 2³ = 21356465513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21356465591) 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, 6246526 + ... + 6249943.

It is an arithmetic number, because the mean of its divisors is an integer number (5342240925).

Almost surely, 2^21356465521 is an apocalyptic number.

It is an amenable number.

21356465521 is a deficient number, since it is larger than the sum of its proper divisors (12498179).

21356465521 is a wasteful number, since it uses less digits than its factorization.

21356465521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12498178.

The product of its digits is 216000, while the sum is 40.

The spelling of 21356465521 in words is "twenty-one billion, three hundred fifty-six million, four hundred sixty-five thousand, five hundred twenty-one".