216561066521 has 2 divisors, whose sum is σ = 216561066522. Its totient is φ = 216561066520.

The previous prime is 216561066503. The next prime is 216561066551. The reversal of 216561066521 is 125660165612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 191724882496 + 24836184025 = 437864^2 + 157595^2 .

It is a cyclic number.

It is not a de Polignac number, because 216561066521 - 2⁶ = 216561066457 is a prime.

It is not a weakly prime, because it can be changed into another prime (216561066551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108280533260 + 108280533261.

It is an arithmetic number, because the mean of its divisors is an integer number (108280533261).

Almost surely, 2^216561066521 is an apocalyptic number.

It is an amenable number.

216561066521 is a deficient number, since it is larger than the sum of its proper divisors (1).

216561066521 is an equidigital number, since it uses as much as digits as its factorization.

216561066521 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 129600, while the sum is 41.

Subtracting from 216561066521 its reverse (125660165612), we obtain a palindrome (90900900909).

The spelling of 216561066521 in words is "two hundred sixteen billion, five hundred sixty-one million, sixty-six thousand, five hundred twenty-one".