644026 has 4 divisors (see below), whose sum is σ = 966042. Its totient is φ = 322012.

The previous prime is 644009. The next prime is 644029. The reversal of 644026 is 620446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 620446 = 2 ⋅310223.

It can be written as a sum of positive squares in only one way, i.e., 638401 + 5625 = 799^2 + 75^2 .

It is a junction number, because it is equal to n+sod(n) for n = 643988 and 644006.

It is not an unprimeable number, because it can be changed into a prime (644029) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 161005 + ... + 161008.

2⁶⁴⁴⁰²⁶ is an apocalyptic number.

644026 is a deficient number, since it is larger than the sum of its proper divisors (322016).

644026 is a wasteful number, since it uses less digits than its factorization.

644026 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 322015.

The product of its (nonzero) digits is 1152, while the sum is 22.

The square root of 644026 is about 802.5123052016. The cubic root of 644026 is about 86.3577132175.

The spelling of 644026 in words is "six hundred forty-four thousand, twenty-six".