213721 has 2 divisors, whose sum is σ = 213722. Its totient is φ = 213720.

The previous prime is 213713. The next prime is 213727. The reversal of 213721 is 127312.

It is a happy number.

213721 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., 132496 + 81225 = 364^2 + 285^2 .

It is a cyclic number.

It is not a de Polignac number, because 213721 - 2³ = 213713 is a prime.

213721 is a lucky number.

It is equal to p₁₉₁₀₅ and since 213721 and 19105 have the same sum of digits, it is a Honaker prime.

It is a junction number, because it is equal to n+sod(n) for n = 213695 and 213704.

It is not a weakly prime, because it can be changed into another prime (213727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 106860 + 106861.

It is an arithmetic number, because the mean of its divisors is an integer number (106861).

2²¹³⁷²¹ is an apocalyptic number.

It is an amenable number.

213721 is a deficient number, since it is larger than the sum of its proper divisors (1).

213721 is an equidigital number, since it uses as much as digits as its factorization.

213721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 84, while the sum is 16.

The square root of 213721 is about 462.2996863507. The cubic root of 213721 is about 59.7882349535.

The spelling of 213721 in words is "two hundred thirteen thousand, seven hundred twenty-one".