640721213 has 4 divisors (see below), whose sum is σ = 698968608. Its totient is φ = 582473820.

The previous prime is 640721209. The next prime is 640721231. The reversal of 640721213 is 312127046.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 640721213 - 2² = 640721209 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 (640721203) 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 in 3 ways as a sum of consecutive naturals, for example, 29123681 + ... + 29123702.

It is an arithmetic number, because the mean of its divisors is an integer number (174742152).

Almost surely, 2^640721213 is an apocalyptic number.

It is an amenable number.

640721213 is a deficient number, since it is larger than the sum of its proper divisors (58247395).

640721213 is a wasteful number, since it uses less digits than its factorization.

640721213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58247394.

The product of its (nonzero) digits is 2016, while the sum is 26.

The square root of 640721213 is about 25312.4714913420. The cubic root of 640721213 is about 862.0974641403.

Adding to 640721213 its reverse (312127046), we get a palindrome (952848259).

The spelling of 640721213 in words is "six hundred forty million, seven hundred twenty-one thousand, two hundred thirteen".