640817 has 4 divisors (see below), whose sum is σ = 642420. Its totient is φ = 639216.

The previous prime is 640793. The next prime is 640837. The reversal of 640817 is 718046.

640817 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 179776 + 461041 = 424^2 + 679^2 .

It is a cyclic number.

It is not a de Polignac number, because 640817 - 2¹² = 636721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640837) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 359 + ... + 1187.

It is an arithmetic number, because the mean of its divisors is an integer number (160605).

2⁶⁴⁰⁸¹⁷ is an apocalyptic number.

It is an amenable number.

640817 is a deficient number, since it is larger than the sum of its proper divisors (1603).

640817 is an equidigital number, since it uses as much as digits as its factorization.

640817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1602.

The product of its (nonzero) digits is 1344, while the sum is 26.

The square root of 640817 is about 800.5104621428. The cubic root of 640817 is about 86.2140422822.

The spelling of 640817 in words is "six hundred forty thousand, eight hundred seventeen".