219721 has 2 divisors, whose sum is σ = 219722. Its totient is φ = 219720.

The previous prime is 219707. The next prime is 219727. The reversal of 219721 is 127912.

219721 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., 164025 + 55696 = 405^2 + 236^2 .

It is a cyclic number.

It is not a de Polignac number, because 219721 - 2⁵ = 219689 is a prime.

It is a nialpdrome in base 8.

It is a junction number, because it is equal to n+sod(n) for n = 219692 and 219701.

It is not a weakly prime, because it can be changed into another prime (219727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109860 + 109861.

It is an arithmetic number, because the mean of its divisors is an integer number (109861).

2²¹⁹⁷²¹ is an apocalyptic number.

It is an amenable number.

219721 is a deficient number, since it is larger than the sum of its proper divisors (1).

219721 is an equidigital number, since it uses as much as digits as its factorization.

219721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 252, while the sum is 22.

The square root of 219721 is about 468.7440666291. The cubic root of 219721 is about 60.3425773273.

Subtracting from 219721 its reverse (127912), we obtain a square (91809 = 303²).

The spelling of 219721 in words is "two hundred nineteen thousand, seven hundred twenty-one".