205421 has 2 divisors, whose sum is σ = 205422. Its totient is φ = 205420.

The previous prime is 205417. The next prime is 205423. The reversal of 205421 is 124502.

205421 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., 198025 + 7396 = 445^2 + 86^2 .

It is a cyclic number.

It is not a de Polignac number, because 205421 - 2² = 205417 is a prime.

Together with 205423, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 205396 and 205405.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (205423) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 102710 + 102711.

It is an arithmetic number, because the mean of its divisors is an integer number (102711).

2²⁰⁵⁴²¹ is an apocalyptic number.

It is an amenable number.

205421 is a deficient number, since it is larger than the sum of its proper divisors (1).

205421 is an equidigital number, since it uses as much as digits as its factorization.

205421 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 80, while the sum is 14.

The square root of 205421 is about 453.2339351814. The cubic root of 205421 is about 59.0040215587.

Adding to 205421 its reverse (124502), we get a palindrome (329923).

It can be divided in two parts, 2054 and 21, that multiplied together give a palindrome (43134).

The spelling of 205421 in words is "two hundred five thousand, four hundred twenty-one".