221621 has 2 divisors, whose sum is σ = 221622. Its totient is φ = 221620.

The previous prime is 221603. The next prime is 221623. The reversal of 221621 is 126122.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 192721 + 28900 = 439^2 + 170^2 .

It is a cyclic number.

It is not a de Polignac number, because 221621 - 2¹⁴ = 205237 is a prime.

It is a Sophie Germain prime.

Together with 221623, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 221596 and 221605.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (221623) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110810 + 110811.

It is an arithmetic number, because the mean of its divisors is an integer number (110811).

2²²¹⁶²¹ is an apocalyptic number.

It is an amenable number.

221621 is a deficient number, since it is larger than the sum of its proper divisors (1).

221621 is an equidigital number, since it uses as much as digits as its factorization.

221621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 48, while the sum is 14.

The square root of 221621 is about 470.7663964218. The cubic root of 221621 is about 60.5160124272.

Adding to 221621 its reverse (126122), we get a palindrome (347743).

The spelling of 221621 in words is "two hundred twenty-one thousand, six hundred twenty-one".