221666106565609 has 2 divisors, whose sum is σ = 221666106565610. Its totient is φ = 221666106565608.

The previous prime is 221666106565489. The next prime is 221666106565621. The reversal of 221666106565609 is 906565601666122.

221666106565609 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 210725868960000 + 10940237605609 = 14516400^2 + 3307603^2 .

It is a cyclic number.

It is not a de Polignac number, because 221666106565609 - 2¹³ = 221666106557417 is a prime.

It is not a weakly prime, because it can be changed into another prime (221666106565649) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110833053282804 + 110833053282805.

It is an arithmetic number, because the mean of its divisors is an integer number (110833053282805).

Almost surely, 2^{221666106565609} is an apocalyptic number.

It is an amenable number.

221666106565609 is a deficient number, since it is larger than the sum of its proper divisors (1).

221666106565609 is an equidigital number, since it uses as much as digits as its factorization.

221666106565609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 41990400, while the sum is 61.

The spelling of 221666106565609 in words is "two hundred twenty-one trillion, six hundred sixty-six billion, one hundred six million, five hundred sixty-five thousand, six hundred nine".