1720321 has 2 divisors, whose sum is σ = 1720322. Its totient is φ = 1720320.

The previous prime is 1720307. The next prime is 1720339. The reversal of 1720321 is 1230271.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1718721 + 1600 = 1311^2 + 40^2 .

It is a cyclic number.

It is not a de Polignac number, because 1720321 - 2⁵ = 1720289 is a prime.

1720321 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 1720295 and 1720304.

It is not a weakly prime, because it can be changed into another prime (1720361) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 860160 + 860161.

It is an arithmetic number, because the mean of its divisors is an integer number (860161).

It is a Proth number, since it is equal to 105 ⋅ 2¹⁴ + 1 and 105 < 2¹⁴.

2^1720321 is an apocalyptic number.

It is an amenable number.

1720321 is a deficient number, since it is larger than the sum of its proper divisors (1).

1720321 is an equidigital number, since it uses as much as digits as its factorization.

1720321 is an odious number, because the sum of its binary digits is odd.

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

The square root of 1720321 is about 1311.6100792537. The cubic root of 1720321 is about 119.8219814125.

Adding to 1720321 its reverse (1230271), we get a palindrome (2950592).

The spelling of 1720321 in words is "one million, seven hundred twenty thousand, three hundred twenty-one".