209621 has 2 divisors, whose sum is σ = 209622. Its totient is φ = 209620.

The previous prime is 209597. The next prime is 209623. The reversal of 209621 is 126902.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 192721 + 16900 = 439^2 + 130^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-209621 is a prime.

Together with 209623, 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 = 209593 and 209602.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (209623) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104810 + 104811.

It is an arithmetic number, because the mean of its divisors is an integer number (104811).

2²⁰⁹⁶²¹ is an apocalyptic number.

It is an amenable number.

209621 is a deficient number, since it is larger than the sum of its proper divisors (1).

209621 is an equidigital number, since it uses as much as digits as its factorization.

209621 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 216, while the sum is 20.

The square root of 209621 is about 457.8438598474. The cubic root of 209621 is about 59.4034401149.

The spelling of 209621 in words is "two hundred nine thousand, six hundred twenty-one".