640021351 has 2 divisors, whose sum is σ = 640021352. Its totient is φ = 640021350.

The previous prime is 640021309. The next prime is 640021363. The reversal of 640021351 is 153120046.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640021351 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640022351) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320010675 + 320010676.

It is an arithmetic number, because the mean of its divisors is an integer number (320010676).

Almost surely, 2^640021351 is an apocalyptic number.

640021351 is a deficient number, since it is larger than the sum of its proper divisors (1).

640021351 is an equidigital number, since it uses as much as digits as its factorization.

640021351 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 640021351 is about 25298.6432640171. The cubic root of 640021351 is about 861.7834591010.

Adding to 640021351 its reverse (153120046), we get a palindrome (793141397).

The spelling of 640021351 in words is "six hundred forty million, twenty-one thousand, three hundred fifty-one".