1721009 has 2 divisors, whose sum is σ = 1721010. Its totient is φ = 1721008.

The previous prime is 1721003. The next prime is 1721011. The reversal of 1721009 is 9001271.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1056784 + 664225 = 1028^2 + 815^2 .

It is a cyclic number.

It is not a de Polignac number, because 1721009 - 2¹⁶ = 1655473 is a prime.

Together with 1721011, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (1721003) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 860504 + 860505.

It is an arithmetic number, because the mean of its divisors is an integer number (860505).

2^1721009 is an apocalyptic number.

It is an amenable number.

1721009 is a deficient number, since it is larger than the sum of its proper divisors (1).

1721009 is an equidigital number, since it uses as much as digits as its factorization.

1721009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 126, while the sum is 20.

The square root of 1721009 is about 1311.8723261049. The cubic root of 1721009 is about 119.8379525667.

The spelling of 1721009 in words is "one million, seven hundred twenty-one thousand, nine".