640055021 has 4 divisors (see below), whose sum is σ = 648822972. Its totient is φ = 631287072.

The previous prime is 640054993. The next prime is 640055023. The reversal of 640055021 is 120550046.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 280194121 + 359860900 = 16739^2 + 18970^2 .

It is a cyclic number.

It is not a de Polignac number, because 640055021 - 2²² = 635860717 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640055023) 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 in 3 ways as a sum of consecutive naturals, for example, 4383866 + ... + 4384011.

It is an arithmetic number, because the mean of its divisors is an integer number (162205743).

Almost surely, 2^640055021 is an apocalyptic number.

It is an amenable number.

640055021 is a deficient number, since it is larger than the sum of its proper divisors (8767951).

640055021 is an equidigital number, since it uses as much as digits as its factorization.

640055021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8767950.

The product of its (nonzero) digits is 1200, while the sum is 23.

The square root of 640055021 is about 25299.3087059706. The cubic root of 640055021 is about 861.7985709616.

The spelling of 640055021 in words is "six hundred forty million, fifty-five thousand, twenty-one".