640621 has 2 divisors, whose sum is σ = 640622. Its totient is φ = 640620.

The previous prime is 640613. The next prime is 640631. The reversal of 640621 is 126046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 469225 + 171396 = 685^2 + 414^2 .

It is a cyclic number.

It is not a de Polignac number, because 640621 - 2³ = 640613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640631) 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, 320310 + 320311.

It is an arithmetic number, because the mean of its divisors is an integer number (320311).

2⁶⁴⁰⁶²¹ is an apocalyptic number.

It is an amenable number.

640621 is a deficient number, since it is larger than the sum of its proper divisors (1).

640621 is an equidigital number, since it uses as much as digits as its factorization.

640621 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 640621 is about 800.3880308950. The cubic root of 640621 is about 86.2052515898.

Adding to 640621 its reverse (126046), we get a palindrome (766667).

The spelling of 640621 in words is "six hundred forty thousand, six hundred twenty-one".