211661 has 2 divisors, whose sum is σ = 211662. Its totient is φ = 211660.
The previous prime is 211657. The next prime is 211663. The reversal of 211661 is 166112.
It is a happy number.
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 175561 + 36100 = 419^2 + 190^2 .
It is a cyclic number.
It is not a de Polignac number, because 211661 - 22 = 211657 is a prime.
It is a Sophie Germain prime.
Together with 211663, it forms a pair of twin primes.
It is a Chen prime.
It is a Curzon number.
It is a plaindrome in base 16.
It is a congruent number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 211661.
It is not a weakly prime, because it can be changed into another prime (211663) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (11) of ones.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 105830 + 105831.
It is an arithmetic number, because the mean of its divisors is an integer number (105831).
2211661 is an apocalyptic number.
It is an amenable number.
211661 is a deficient number, since it is larger than the sum of its proper divisors (1).
211661 is an equidigital number, since it uses as much as digits as its factorization.
211661 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 72, while the sum is 17.
The square root of 211661 is about 460.0662995700. The cubic root of 211661 is about 59.5955201353.
Adding to 211661 its reverse (166112), we get a palindrome (377773).
The spelling of 211661 in words is "two hundred eleven thousand, six hundred sixty-one".
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