721637321 has 2 divisors, whose sum is σ = 721637322. Its totient is φ = 721637320.

The previous prime is 721637311. The next prime is 721637359. The reversal of 721637321 is 123736127.

721637321 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 499030921 + 222606400 = 22339^2 + 14920^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-721637321 is a prime.

It is not a weakly prime, because it can be changed into another prime (721637311) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360818660 + 360818661.

It is an arithmetic number, because the mean of its divisors is an integer number (360818661).

Almost surely, 2^721637321 is an apocalyptic number.

It is an amenable number.

721637321 is a deficient number, since it is larger than the sum of its proper divisors (1).

721637321 is an equidigital number, since it uses as much as digits as its factorization.

721637321 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10584, while the sum is 32.

The square root of 721637321 is about 26863.3080799815. The cubic root of 721637321 is about 896.9598329368.

The spelling of 721637321 in words is "seven hundred twenty-one million, six hundred thirty-seven thousand, three hundred twenty-one".