640729 has 4 divisors (see below), whose sum is σ = 658084. Its totient is φ = 623376.

The previous prime is 640727. The next prime is 640733. The reversal of 640729 is 927046.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 927046 = 2 ⋅463523.

It can be written as a sum of positive squares in 2 ways, for example, as 559504 + 81225 = 748^2 + 285^2 .

It is not a de Polignac number, because 640729 - 2¹ = 640727 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 640697 and 640706.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8622 + ... + 8695.

It is an arithmetic number, because the mean of its divisors is an integer number (164521).

2⁶⁴⁰⁷²⁹ is an apocalyptic number.

It is an amenable number.

640729 is a deficient number, since it is larger than the sum of its proper divisors (17355).

640729 is a wasteful number, since it uses less digits than its factorization.

640729 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17354.

The product of its (nonzero) digits is 3024, while the sum is 28.

The square root of 640729 is about 800.4554953275. The cubic root of 640729 is about 86.2100956624.

It can be divided in two parts, 640 and 729, that added together give a square (1369 = 37²).

The spelling of 640729 in words is "six hundred forty thousand, seven hundred twenty-nine".