640202021 has 2 divisors, whose sum is σ = 640202022. Its totient is φ = 640202020.

The previous prime is 640202011. The next prime is 640202023. The reversal of 640202021 is 120202046.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 357625921 + 282576100 = 18911^2 + 16810^2 .

It is a cyclic number.

It is not a de Polignac number, because 640202021 - 2⁶ = 640201957 is a prime.

Together with 640202023, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640202023) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320101010 + 320101011.

It is an arithmetic number, because the mean of its divisors is an integer number (320101011).

Almost surely, 2^640202021 is an apocalyptic number.

It is an amenable number.

640202021 is a deficient number, since it is larger than the sum of its proper divisors (1).

640202021 is an equidigital number, since it uses as much as digits as its factorization.

640202021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 192, while the sum is 17.

The square root of 640202021 is about 25302.2137569028. The cubic root of 640202021 is about 861.8645416925.

Adding to 640202021 its reverse (120202046), we get a palindrome (760404067).

The spelling of 640202021 in words is "six hundred forty million, two hundred two thousand, twenty-one".