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231821 is a prime number

231821 has 2 divisors, whose sum is σ = 231822. Its totient is φ = 231820.

The previous prime is 231809. The next prime is 231823. The reversal of 231821 is 128132.

Adding to 231821 its reverse (128132), we get a palindrome (359953).

231821 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., 133225 + 98596 = 365^2 + 314^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2k-231821 is a prime.

It is a Sophie Germain prime.

Together with 231823, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 231821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (231823) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 115910 + 115911.

It is an arithmetic number, because the mean of its divisors is an integer number (115911).

2231821 is an apocalyptic number.

It is an amenable number.

231821 is a deficient number, since it is larger than the sum of its proper divisors (1).

231821 is an equidigital number, since it uses as much as digits as its factorization.

231821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 96, while the sum is 17.

The square root of 231821 is about 481.4779330354. The cubic root of 231821 is about 61.4305294387.

The spelling of 231821 in words is "two hundred thirty-one thousand, eight hundred twenty-one".