641821 has 2 divisors, whose sum is σ = 641822. Its totient is φ = 641820.

The previous prime is 641819. The next prime is 641827. The reversal of 641821 is 128146.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 617796 + 24025 = 786^2 + 155^2 .

It is a cyclic number.

It is not a de Polignac number, because 641821 - 2¹ = 641819 is a prime.

Together with 641819, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 641792 and 641801.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (641827) 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, 320910 + 320911.

It is an arithmetic number, because the mean of its divisors is an integer number (320911).

2⁶⁴¹⁸²¹ is an apocalyptic number.

It is an amenable number.

641821 is a deficient number, since it is larger than the sum of its proper divisors (1).

641821 is an equidigital number, since it uses as much as digits as its factorization.

641821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 384, while the sum is 22.

The square root of 641821 is about 801.1373165694. The cubic root of 641821 is about 86.2590440702.

Adding to 641821 its reverse (128146), we get a palindrome (769967).

The spelling of 641821 in words is "six hundred forty-one thousand, eight hundred twenty-one".