216509599921 has 4 divisors (see below), whose sum is σ = 216529790500. Its totient is φ = 216489409344.

The previous prime is 216509599897. The next prime is 216509599937. The reversal of 216509599921 is 129995905612.

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 130725633600 + 85783966321 = 361560^2 + 292889^2 .

It is a cyclic number.

It is not a de Polignac number, because 216509599921 - 2¹⁷ = 216509468849 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (216509599961) 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, 10079196 + ... + 10100653.

It is an arithmetic number, because the mean of its divisors is an integer number (54132447625).

Almost surely, 2^216509599921 is an apocalyptic number.

It is an amenable number.

216509599921 is a deficient number, since it is larger than the sum of its proper divisors (20190579).

216509599921 is a wasteful number, since it uses less digits than its factorization.

216509599921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20190578.

The product of its (nonzero) digits is 3936600, while the sum is 58.

The spelling of 216509599921 in words is "two hundred sixteen billion, five hundred nine million, five hundred ninety-nine thousand, nine hundred twenty-one".