721631 has 2 divisors, whose sum is σ = 721632. Its totient is φ = 721630.

The previous prime is 721621. The next prime is 721661. The reversal of 721631 is 136127.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 721631 - 2¹⁰ = 720607 is a prime.

It is a super-2 number, since 2×721631² = 1041502600322, which contains 22 as substring.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 721631.

It is not a weakly prime, because it can be changed into another prime (721621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360815 + 360816.

It is an arithmetic number, because the mean of its divisors is an integer number (360816).

2⁷²¹⁶³¹ is an apocalyptic number.

721631 is a deficient number, since it is larger than the sum of its proper divisors (1).

721631 is an equidigital number, since it uses as much as digits as its factorization.

721631 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 252, while the sum is 20.

The square root of 721631 is about 849.4886697302. The cubic root of 721631 is about 89.6957214031.

Adding to 721631 its reverse (136127), we get a palindrome (857758).

The spelling of 721631 in words is "seven hundred twenty-one thousand, six hundred thirty-one".