243216661 has 2 divisors, whose sum is σ = 243216662. Its totient is φ = 243216660.

The previous prime is 243216641. The next prime is 243216683. The reversal of 243216661 is 166612342.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 218862436 + 24354225 = 14794^2 + 4935^2 .

It is a cyclic number.

It is not a de Polignac number, because 243216661 - 2¹⁵ = 243183893 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (243216601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 121608330 + 121608331.

It is an arithmetic number, because the mean of its divisors is an integer number (121608331).

Almost surely, 2^243216661 is an apocalyptic number.

It is an amenable number.

243216661 is a deficient number, since it is larger than the sum of its proper divisors (1).

243216661 is an equidigital number, since it uses as much as digits as its factorization.

243216661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10368, while the sum is 31.

The square root of 243216661 is about 15595.4051245872. The cubic root of 243216661 is about 624.2105539798.

The spelling of 243216661 in words is "two hundred forty-three million, two hundred sixteen thousand, six hundred sixty-one".