640250021 has 2 divisors, whose sum is σ = 640250022. Its totient is φ = 640250020.

The previous prime is 640249997. The next prime is 640250029. The reversal of 640250021 is 120052046.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 406465921 + 233784100 = 20161^2 + 15290^2 .

It is a cyclic number.

It is not a de Polignac number, because 640250021 - 2²⁶ = 573141157 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 640249975 and 640250002.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640250029) 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, 320125010 + 320125011.

It is an arithmetic number, because the mean of its divisors is an integer number (320125011).

Almost surely, 2^640250021 is an apocalyptic number.

It is an amenable number.

640250021 is a deficient number, since it is larger than the sum of its proper divisors (1).

640250021 is an equidigital number, since it uses as much as digits as its factorization.

640250021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 480, while the sum is 20.

The square root of 640250021 is about 25303.1622727279. The cubic root of 640250021 is about 861.8860809685.

The spelling of 640250021 in words is "six hundred forty million, two hundred fifty thousand, twenty-one".