216661 has 2 divisors, whose sum is σ = 216662. Its totient is φ = 216660.

The previous prime is 216653. The next prime is 216679. The reversal of 216661 is 166612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 202500 + 14161 = 450^2 + 119^2 .

It is a cyclic number.

It is not a de Polignac number, because 216661 - 2³ = 216653 is a prime.

It is a Chen prime.

It is equal to p₁₉₃₃₆ and since 216661 and 19336 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108330 + 108331.

It is an arithmetic number, because the mean of its divisors is an integer number (108331).

2²¹⁶⁶⁶¹ is an apocalyptic number.

It is an amenable number.

216661 is a deficient number, since it is larger than the sum of its proper divisors (1).

216661 is an equidigital number, since it uses as much as digits as its factorization.

216661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 432, while the sum is 22.

The square root of 216661 is about 465.4685811094. The cubic root of 216661 is about 60.0611413781.

The spelling of 216661 in words is "two hundred sixteen thousand, six hundred sixty-one".