721421 has 4 divisors (see below), whose sum is σ = 723132. Its totient is φ = 719712.

The previous prime is 721397. The next prime is 721439. The reversal of 721421 is 124127.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 373321 + 348100 = 611^2 + 590^2 .

It is a cyclic number.

It is not a de Polignac number, because 721421 - 2¹⁰ = 720397 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 721421.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721451) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 281 + ... + 1233.

It is an arithmetic number, because the mean of its divisors is an integer number (180783).

2⁷²¹⁴²¹ is an apocalyptic number.

It is an amenable number.

721421 is a deficient number, since it is larger than the sum of its proper divisors (1711).

721421 is an equidigital number, since it uses as much as digits as its factorization.

721421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1710.

The product of its digits is 112, while the sum is 17.

The square root of 721421 is about 849.3650569690. The cubic root of 721421 is about 89.6870198512.

Adding to 721421 its reverse (124127), we get a palindrome (845548).

The spelling of 721421 in words is "seven hundred twenty-one thousand, four hundred twenty-one", and thus it is an iban number.