621721 has 2 divisors, whose sum is σ = 621722. Its totient is φ = 621720.

The previous prime is 621703. The next prime is 621739. The reversal of 621721 is 127126.

It is a balanced prime because it is at equal distance from previous prime (621703) and next prime (621739).

It can be written as a sum of positive squares in only one way, i.e., 583696 + 38025 = 764^2 + 195^2 .

It is a cyclic number.

It is not a de Polignac number, because 621721 - 2¹⁵ = 588953 is a prime.

It is a Chen prime.

621721 is a lucky number.

It is a nialpdrome in base 15.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (621701) 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, 310860 + 310861.

It is an arithmetic number, because the mean of its divisors is an integer number (310861).

2⁶²¹⁷²¹ is an apocalyptic number.

It is an amenable number.

621721 is a deficient number, since it is larger than the sum of its proper divisors (1).

621721 is an equidigital number, since it uses as much as digits as its factorization.

621721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 168, while the sum is 19.

The square root of 621721 is about 788.4928661694. The cubic root of 621721 is about 85.3490147912.

Adding to 621721 its reverse (127126), we get a palindrome (748847).

The spelling of 621721 in words is "six hundred twenty-one thousand, seven hundred twenty-one".