721321 has 2 divisors, whose sum is σ = 721322. Its totient is φ = 721320.

The previous prime is 721319. The next prime is 721333. The reversal of 721321 is 123127.

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., 403225 + 318096 = 635^2 + 564^2 .

It is an emirp because it is prime and its reverse (123127) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 721321 - 2¹ = 721319 is a prime.

Together with 721319, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 721295 and 721304.

It is not a weakly prime, because it can be changed into another prime (721351) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360660 + 360661.

It is an arithmetic number, because the mean of its divisors is an integer number (360661).

2⁷²¹³²¹ is an apocalyptic number.

It is an amenable number.

721321 is a deficient number, since it is larger than the sum of its proper divisors (1).

721321 is an equidigital number, since it uses as much as digits as its factorization.

721321 is an evil number, because the sum of its binary digits is even.

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

The square root of 721321 is about 849.3061874259. The cubic root of 721321 is about 89.6828756615.

Adding to 721321 its reverse (123127), we get a palindrome (844448).

The spelling of 721321 in words is "seven hundred twenty-one thousand, three hundred twenty-one", and thus it is an iban number.