217216661 has 2 divisors, whose sum is σ = 217216662. Its totient is φ = 217216660.

The previous prime is 217216621. The next prime is 217216691. The reversal of 217216661 is 166612712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 171112561 + 46104100 = 13081^2 + 6790^2 .

It is a cyclic number.

It is not a de Polignac number, because 217216661 - 2¹⁰ = 217215637 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (217216621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108608330 + 108608331.

It is an arithmetic number, because the mean of its divisors is an integer number (108608331).

Almost surely, 2^217216661 is an apocalyptic number.

It is an amenable number.

217216661 is a deficient number, since it is larger than the sum of its proper divisors (1).

217216661 is an equidigital number, since it uses as much as digits as its factorization.

217216661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6048, while the sum is 32.

The square root of 217216661 is about 14738.2719814773. The cubic root of 217216661 is about 601.1244294108.

It can be divided in two parts, 21721 and 6661, that added together give a palindrome (28382).

The spelling of 217216661 in words is "two hundred seventeen million, two hundred sixteen thousand, six hundred sixty-one".